NOAA's Response and Restoration Blog

An inside look at the science of cleaning up and fixing the mess of marine pollution

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Science of Oil Spills Training Now Accepting Applications for Spring 2016

Two people closely examining rocks and seaweed on a shoreline.

These classes help prepare responders to understand the environmental risks and scientific considerations when addressing oil spills, and also include a field trip to a local beach to apply newly learned skills. (NOAA)

NOAA‘s Office of Response and Restoration, a leader in providing scientific information in response to marine pollution, has scheduled Science of Oil Spills (SOS) classes in two locations in spring 2016:

  • Mobile, Alabama the week of March 28, 2016
  • Ann Arbor, Michigan the week of May 16, 2016

We will accept applications for these classes as follows:

For the Mobile class, the application period will be open until Friday, January 22. We will notify accepted participants by email no later than Friday, February 5.

For the Ann Arbor class, the application period will be open until Friday, March 11. We will notify accepted participants by email no later than Friday, March 25.

SOS classes help spill responders increase their understanding of oil spill science when analyzing spills and making risk-based decisions. They are designed for new and mid-level spill responders.

These trainings cover:

  • Fate and behavior of oil spilled in the environment.
  • An introduction to oil chemistry and toxicity.
  • A review of basic spill response options for open water and shorelines.
  • Spill case studies.
  • Principles of ecological risk assessment.
  • A field trip.
  • An introduction to damage assessment techniques.
  • Determining cleanup endpoints.

To view the topics for the next SOS class, download a sample agenda [PDF, 170 KB].

Please understand that classes are not filled on a first-come, first-served basis. We try to diversify the participant composition to ensure a variety of perspectives and experiences, to enrich the workshop for the benefit of all participants. Classes are generally limited to 40 participants.

For more information, and to learn how to apply for the class, visit the SOS Classes page.

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Births Down and Deaths Up in Gulf Dolphins Affected by Deepwater Horizon Oil Spill

A mother bottlenose dolphin pushes her dead newborn calf at the water's surface.

Dolphin Y01 pushes a dead calf through the waters of Barataria Bay, Louisiana, in March 2013. This behavior is sometimes observed in female dolphins when their newborn calf does not survive. Barataria Bay dolphins have seen a disturbingly low rate of reproductive success in the wake of the Deepwater Horizon oil spill. (Louisiana Department of Wildlife and Fisheries)

In August of 2011, a team of independent and government scientists evaluating the health of bottlenose dolphins in Louisiana’s Barataria Bay gave dolphin Y35 a good health outlook.

Based on the ultrasound, she was in the early stages of pregnancy, but unlike many of the other dolphins examined that summer day, Y35 was in pretty good shape. She wasn’t extremely underweight or suffering from moderate-to-severe lung disease, conditions connected to exposure to Deepwater Horizon oil in the heavily impacted Barataria Bay.

Veterinarians did note, however, that she had alarmingly low levels of important stress hormones responsible for behaviors such as the fight-or-flight response. Normal levels of these hormones help animals cope with stressful situations. This rare condition—known as hypoadrenocorticism—had never been reported before in dolphins, which is why it was not used for Y35 and the other dolphins’ health prognoses.

Less than six months later, researchers spotted Y35 for the last time. It was only 16 days before her expected due date. She and her calf are now both presumed dead, a disturbingly common trend among the bottlenose dolphins that call Barataria Bay their year-round home.

This trend of reproductive failure and death in Gulf dolphins over five years of monitoring after the 2010 Deepwater Horizon oil spill is outlined in a November 2015 study led by NOAA and published in the peer-reviewed journal Proceedings of the Royal Society.

Of the 10 Barataria Bay dolphins confirmed to be pregnant during the 2011 health assessment, only two successfully gave birth to calves that have survived. This unusually low rate of reproductive success—only 20%—stands in contrast to the 83% success rate in the generally healthier dolphins being studied in Florida’s Sarasota Bay, an area not affected by Deepwater Horizon oil.

Baby Bump in Failed Pregnancies

While hypoadrenocorticism had not been documented previously in dolphins, it has been found in humans. In human mothers with this condition, pregnancy and birth—stressful and risky enough conditions on their own—can be life-threatening for both mother and child when the condition is left untreated. Wild dolphins with this condition would be in a similar situation.

Mink exposed to oil in an experiment ended up exhibiting very low levels of stress hormones, while sea otters exposed to the Exxon Valdez oil spill experienced high rates of failed pregnancies and pup death. These cases are akin to what scientists have observed in the dolphins of Barataria Bay after the Deepwater Horizon oil spill.

Among the pregnant dolphins being monitored in this study, at least two lost their calves before giving birth. Veterinarians confirmed with ultrasound that one of these dolphins, Y31, was carrying a dead calf in utero during her 2011 exam. Another pregnant dolphin, Y01, did not successfully give birth in 2012, and was then seen pushing a dead newborn calf in 2013. Given that dolphins have a gestation of over 12 months, this means Y01 had two failed pregnancies in a row.

The other five dolphins to lose their calves after the Deepwater Horizon oil spill, excluding Y35, survived pregnancy themselves but were seen again and again in the months after their due dates without any young. Dolphin calves stick close to their mothers’ sides in the first two or three months after birth, indicating that these pregnant dolphins also had calves that did not survive.

At least half of the dolphins with failed pregnancies also suffered from moderate-to-severe lung disease, a symptom associated with exposure to petroleum products. The only two dolphins to give birth to healthy calves had relatively minor lung conditions.

Survival of the Least Oiled

Dolphin Y35 wasn’t the only one of the 32 dolphins being monitored in Barataria Bay to disappear in the months following her 2011 examination. Three others were never sighted again in the 15 straight surveys tracking these dolphins. Or rather, they were never seen again alive. One of them, Y12, was a 16-year-old adult male whose emaciated carcass washed up in Louisiana only a few weeks before the pregnant Y35 was last seen. In fact, the number of dolphins washing up dead in Barataria Bay from August 2010 through 2011 was the highest ever recorded for that area.

Survival rate in this group of dolphins was estimated at only 86%, down from the 95-96% survival seen in dolphin populations not in contact with Deepwater Horizon oil. The marshy maze of Barataria Bay falls squarely inside the footprint of the Deepwater Horizon oil spill, and its dolphins and others along the northern Gulf Coast have repeatedly been found to be sick and dying in historically high numbers. Considering how deadly this oil spill has been for Gulf bottlenose dolphins and their young, researchers expect recovery for these marine mammals to be a long time coming.

Watch an updated video of the researchers as they temporarily catch and give health exams to some of the dolphins in Barataria Bay, Louisiana, in August of 2011 and read a 2013 Q&A with two of the NOAA researchers involved in these studies:

This study was conducted under the Natural Resource Damage Assessment for the Deepwater Horizon oil spill. These results are included in the injury assessment documented in the Draft Programmatic Assessment and Restoration Plan that is currently out for public comment. We will accept comments on the plan through December 4, 2015.

This research was conducted under the authority of Scientific Research Permit nos. 779-1633 and 932-1905/MA-009526 issued by NOAA’s National Marine Fisheries Service pursuant to the U.S. Marine Mammal Protection Act.

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How Does Oil Get into the Ocean?

Oil rig in the Gulf of Mexico.

Oil rig in the Gulf of Mexico, off the coast of Port Fourchon, Louisiana. A 2003 report from the National Academy of Sciences estimates 3% of the oil entering the ocean each year comes from oil and gas exploration and extraction activities. (NOAA)

When many of us think of oil spills, we might think of an oil tanker running aground and spilling its contents into the ocean, as in the case of the oil tanker Exxon Valdez when the ship ran aground near the coast of Alaska in 1989.

In fact, there are actually several ways crude or refined oil may reach the marine environment. All of those spills add up too. In a 2003 publication, the National Research Council of the National Academy of Sciences reported that roughly 343,200,000 gallons of oil were released into the sea annually, worldwide. Of this amount, the report estimates the origin of that oil as follows:

  • Use or consumption of oil (which includes operational discharges from ships and discharges from land-based sources): 37%
  • Transportation (accidental spills from ships): 12%
  • Extraction: 3%
  • Natural seeps: 46%

Wherever oil is consumed, such as in manufacturing or when loading a ship with fuel, there are opportunities for oil spills. According to the Washington State Department of Ecology [PDF], most spills that occur during ship fueling happen because of inattention, inadequate procedure, procedural error, or poor judgment—in other words, human error.

The typically small-in-size spills that come from consuming oil originate from a variety of activities and actually account for most of the oil spilled by humans into the sea.

When the Exxon Valdez oil spill occurred, on the other hand, crude oil was in transport. Since oil is an international commodity and in constant demand, there are always ships, pipelines, and (increasingly) trains moving it around the world. According to the International Tanker Owners Pollution Federation, occurrences of large spills from tankers and barges (above approximately 2,000 gallons) have decreased dramatically since 1970. This can be attributed at least in part to advances in safety thanks to the Oil Pollution Act of 1990.

While oil extraction is not considered a large source of the overall amount of oil released into the sea each year, spills from offshore oil exploration and drilling can be huge when they do happen. The well blowout that caused Deepwater Horizon spill in the Gulf of Mexico in 2010 is a (very large) example of an oil spill occurring during extraction activities. This type of accident occurs only where oil exploration and drilling operations take place—in the United States, the Gulf of Mexico and waters off the southern California coast are the major areas.

Dark, thick oil seeps out of the ocean floor sediments.

A natural tar seep releases oil offshore from Gaviota, California. When an oil spill occurs in an area with many naturally occurring seeps, responders may have a difficult time telling spilled oil apart from seep oil. (Donna Schroeder/U.S. Geological Survey)

While not technically “oil spills,” oil seeps from the ocean floor naturally release oil from subterranean reservoirs and represent the largest source of oil entering seas both in the United States and around the world. Even though seeps are not without their own impacts on marine life, natural oil seeps release oil slowly over time, allowing ecosystems to adapt. During an oil spill, the amount of oil released in a short time can overwhelm an ecosystem.

Impact, then, is not only determined by how much oil is in the environment, but also the type of oil and how quickly it is released.

The May 2015 oil spill at Refugio State Beach was caused by a pipeline break near Santa Barbara, California, adjacent to Coal Oil Point, a region famous for its natural seeps. Oil from seeps there release an estimated 6,500-7,000 gallons of oil per day (Lorenson et al., 2011) and are among the most active in the world. One of the response challenges during that spill was distinguishing between the oil that flowed directly into the ocean from the pipeline break and that from the ongoing seeps.

For a quick glance at the major causes of oil spills in the ocean, check out our infographic:

Graphic showing buildings and cars using oil, a tanker transporting oil, and a rig drilling for oil in the ocean, with a natural seep leaking oil out of the seafloor. Use of oil: Anywhere crude or refined oil is stored or used, such as for fuel or in manufacturing, there is risk of a spill. Transportation of oil: Crude oil is an international commodity, and as it is moved around the world, it may be spilled from storage tanks, barges, pipelines, and other bulk transport. Extraction of oil: Oil exploration and extraction from the ground or below the ocean surface potentially could release oil into the environment. Natural seeps of oil: Oil seeps are natural leaks of crude oil and gas from subterranean reservoirs through the ocean floor. While not caused by humans, oil from seeps can be confused with oil spills.

There are four primary ways oil can end up in the ocean: natural seeps, consumption, extraction, and transportation of oil. (NOAA)

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How Do Oil Spills Get Cleaned up on Shore?

Beach cleanup crew members use a shovel to place gathered oil and affected sand into a bag on a beach.

Cleaning up oil from shorelines is a messy job. Beach cleanup crew members use a shovel to place gathered oil and affected sand into a bag as they clean up along a beach near Refugio State Beach, California, May 21, 2015. Cleanup teams used shovels and their hands to gather affected soil and ocean debris along oil impacted beaches north of Santa Barbara. (U.S. Coast Guard)

We often say that no two oil spills are alike, but one thing spills have in common is that cleaning oil off of shorelines is a messy business.

If a ship sinks or an oil pipeline ruptures, the primary goals of spill responders are to contain the oil source to stop any (more) oil from leaking and to prevent already spilled oil from spreading. However, weather conditions and ocean currents may overwhelm containment booms and other offshore oil spill response strategies. That means escaping oil may reach shorelines both near to and far from the initial oil spill location.

But when oil stains shorelines, what methods and equipment do responders use to remove it? And how is that different from cleaning up oil out at sea?

Here at NOAA, we have a library full of spill response manuals, technical reports, scientific journal articles, job aids, case histories, and guidance documents describing the methods used to clean up shorelines. And after every major oil spill there are advances in shoreline cleanup methods and equipment.

Here we present some commonly used shoreline cleanup options. Keep in mind that all response options, including what responders call “natural recovery” (letting oil break down naturally in the environment), have potential trade-offs. This means we have to take into consideration the impact of the cleanup methods themselves as we assess the overall environmental impacts of any action.

There are, of course, nuances in cleanup strategies at every oil spill that reflect the specific oil type, local environmental conditions, shoreline habitats, shore access, and a host of safety and logistical considerations. These variables will influence the particular cleanup strategy responders use at any one spill.

And at most oil spills, a combination of cleanup methods will be used (but not necessarily in the order shown here). Let’s take a look at each of these methods.

Responding to oil spills on shore: This graphic shows an overview of people using eight methods for cleaning up oil from shorelines. 1. Shoreling flushing/washing: Water hoses can rinse oil from the shoreline into water, where it can be more easily collected. 2. Booms: Long, floating, interconnected barriers are used to minimize the spread of spilled oil. 3. Vacuums: Industrial-sized vacuum trucks can suction oil from the shoreline or on the water surface. 4. Sorbents: Specialized absorbent materials act like a sponge to pick up oil but not water. 5. Shoreline cleaners and biodegradation agents: Chemical cleaners that act like saops may be used to remove oil, but require special permission. Nutrients may be added to help microbes break down oil. 6. Burning. Also referred to as

Responding to oil spills on shore: This is an overview of the various methods for cleaning up oil from shorelines, from flushing and vacuums to sorbents and heavy machinery. (NOAA)

1) Shoreline Flushing: This method uses water to remove or refloat stranded oil, which allows it to be more easily recovered as a slick on the water. One of the lessons learned from the 1989 Exxon Valdez oil spill was to be very careful about water pressure and temperature to avoid causing more harm to the shoreline.

2) Booms: These long, floating barriers are used to keep spilled oil off the beach, or to collect it after being flushed from the beach into the immediate waters.

3) Vacuums: Large industrial vacuums can suction oil off the beach or shoreline vegetation.

4) Sorbents: These specialized materials, which can take forms such as square pads or long booms, are engineered to absorb oil but not water.

5) Shoreline cleaners and bioremediation agents: There are a variety of chemical cleaners for oiled shorelines that usually require special approval for their use. Surface washing agents [PDF] are used to soften and lift oil off of surfaces or structures that have been oiled, such as beach rocks, docks, and riprap. Bioremediation agents, on the other hand, often take the form of fertilizers that help speed up natural microbial degradation processes. However, conventional cleanup methods (e.g., booms and sorbents) typically are used first to their fullest extent to remove the worst oiling, while these alternative measures usually play a secondary role (if any).

6) Burning: Responders sometimes will perform controlled burns, also referred to as “in situ burning,” of freshly spilled oil floating on the water’s surface or on marsh vegetation.

7) Manual recovery: This method involves using good old buckets, shovels, rakes, and other hand tools to remove oil from shorelines. It is very labor-intensive but is often a primary tool for a response when access for larger equipment is impractical, such as on remote beaches or those without road access.

8) Mechanical removal: When access is possible and won’t cause too much damage to the shoreline, responders may bring in heavy machinery, such as back hoes or front-end loaders, to scoop up and haul away oiled materials in bulk.

Two bobcat digging machines scoop oil from a beach.

Heavy machinery was brought in to remove oil from a beach in Puerto Rico in 2007. (NOAA)

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NOAA Is Supporting Oil Spill Response in Kentucky After Tugs Collide on Mississippi River

On the evening of September 2, 2015, two tug boats collided on the Mississippi River near Columbus, Kentucky, spilling slurry oil into the river.

Early reports, which later may be corrected, indicate an estimated 120,500 gallons of oil were released from a hole in the cargo tank of a barge being towed by the tug Dewey R during the collision. The spill and ensuing response closed the river between mile markers 938 and 922, south of Paducah, Kentucky, but the waterway was reopened to vessel traffic as of September 8.

At the request of the U.S. Coast Guard, NOAA’s Office of Response and Restoration is supporting the response and sending oil spill and data management experts to the scene of the spill. NOAA scientific support coordinators are providing a variety of information for the response, including river flow forecasts, chemistry of the spilled oil, a submerged oil assessment (because this heavier oil may sink), and other information to help determine where the spill will go and what can be done to protect our waterways and keep commerce moving.

The natural resource agencies also are beginning to assess potential impacts to natural resources, a first step to determining whether restoration is needed as a result of the spill.

Updates from NOAA about this oil spill may be available on IncidentNews.

What Is Slurry Oil?

Slurry oil is a residual oil resulting from the refining process and when spilled, most of it will sink or become suspended in the water column. A U.S. Coast Guard overflight the morning of September 3 revealed a floating sheen of oil four to five miles downstream of the discharge, which is not unexpected with this type of heavy oil.

Learn more about different types of oil and their behaviors when spilled and read about a 2005 slurry oil spill in the Gulf of Mexico.

How Is an Oil Spill in a River Different Than One in the Ocean?

From dams and density to muddy waters and vegetation, rivers offer a very different environment than the ocean during an oil spill.

Read more about the kinds of unique challenges we have to consider during an oil spill in a river.

More Information About Oil Spills

Find basic information related to oil spills, cleanup, impacts, and restoration, as well as NOAA’s role during and after oil spills.

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It Took More Than the Exxon Valdez Oil Spill to Pass the Historic Oil Pollution Act of 1990

Aerial view of Exxon Valdez tanker with boom and oil on water.

While the tanker Exxon Valdez spilled nearly 11 million gallons of oil into Alaskan waters, a trifecta of other sizable oil spills followed on its heels. These spills helped pave the way for passage of the Oil Pollution Act of 1990, which would vastly improve oil spill prevention, response, and restoration. (NOAA)

If you, like many, believe oil shouldn’t just be spilled without consequence into the ocean, then you, like us, should be grateful for a very important U.S. law known as the Oil Pollution Act of 1990.

Congress passed this legislation and President George H.W. Bush signed it into law 25 years ago on August 18, 1990, which was the summer after the tanker Exxon Valdez hit ground in Prince William Sound, Alaska. On March 24, 1989, this tanker unleashed almost 11 million gallons of oil into relatively pristine Alaskan waters.

The powerful images from this huge oil spill—streams of dark oil spreading over the water, birds and sea otters coated in oil, workers in shiny plastic suits trying to clean the rocky coastline—both shocked and galvanized the nation. They ultimately motivated the 101st Congress to investigate the causes of recent oil spills, develop guidelines to prevent and clean up pollution, and pass this valuable legislation.

Yet that monumental spill didn’t fully drive home just how inadequate the patchwork of existing federal, state, and local laws were at addressing oil spill prevention, cleanup, liability, and restoration. Nearly a year and a half passed between the Exxon Valdez oil spill and the enactment of the Oil Pollution Act. What happened in the mean time?

The summer of 1989 experienced a trifecta of oil spills that drained any resources left from the ongoing spill response in Alaska. In rapid succession and over the course of less than 24 hours, three other oil tankers poured their cargo into U.S. coastal waters. Between June 23 and 24, the T/V World Prodigy spilled 290,000 gallons of oil in Newport, Rhode Island; the T/V Presidente Rivera emptied 307,000 gallons of oil into the Delaware River; and the T/V Rachel B hit Tank Barge 2514, releasing 239,000 gallons of oil into Texas’s Houston Ship Channel.

But these were far from the only oil spills plaguing U.S. waters during that time. Between the summers of 1989 and 1990, a series of ship collisions, groundings, and pipeline leaks spilled an additional 8 million gallons along the United States coastline. And that doesn’t even include another million gallons of thick fuel oil released from a shore-side facility in the U.S. Virgin Islands after it was damaged by Hurricane Hugo.

Birds killed as a result of oil from the Exxon Valdez spill.

Thanks to the Oil Pollution Act, federal and state agencies can more easily evaluate the full environmental impacts of oil spills — and then enact restoration to make up for that harm. (Exxon Valdez Oil Spill Trustee Council)

Can you imagine—or perhaps remember—sitting at home watching the news and hearing again and again about yet another oil spill? And wondering what the government was going to do about it? Fortunately, in August of 1990, Congress voted unanimously to pass the Oil Pollution Act, which promised—and has largely delivered—significantly improved measures to prevent, prepare for, and respond to oil spills in U.S. waters.

Now, 25 years later, the shipping industry has undergone a makeover in oil spill prevention, preparedness, and response. A couple examples include the phasing out of tankers with easily punctured single hulls and new regulations for driving tankers that require the use of knowledgeable pilots, maneuverable tug escorts, and an appropriate number of people on the ship’s bridge during transit.

Oil spill response research also received a boost thanks to the Oil Pollution Act, which reopened a national research facility dedicated to this topic and shuttered just before the Exxon Valdez spill.

But perhaps one of the most important elements of this law required those responsible for oil spills to foot the bill for both cleaning up the oil and for economic and natural resource damages resulting from it.

This provision also requires oil companies to pay into the Oil Spill Liability Trust Fund, a fund theoretically created by Congress in 1986 but not given the necessary authorization until the Oil Pollution Act of 1990. This fund helps the U.S. Coast Guard—and indirectly, NOAA’s Office of Response and Restoration—pay for the upfront costs of responding to marine and coastal accidents that threaten to release hazardous materials such as oil and also of assessing the potential environmental and cultural impacts (and implementing restoration to make up for them).

This week we’re saying thank you to the Oil Pollution Act by highlighting some of its successes in restoring the environment after oil spills. You can join us on social media using the hashtag #Thanks2OilPollutionAct.

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How Is an Oil Spill in a River Different Than One in the Ocean?

Boat with boom next to oil mixed with river bank vegetation.

The often complex, vegetated banks of rivers can complicate cleaning up oil spills. (NOAA)

Liquid asphalt in the Ohio River. Slurry oil in the Gulf of Mexico. Diesel in an Alaskan stream. Each of these oil spills was very different from each other, partly because they involved very different types of oils.

But even if the same type of oil were spilled in each case, the results would be just as distinct because of where they occurred—one in a large inland river, one in the open ocean, and one in a small coastal creek.

In many cases, oil tends to float. But just because an oil floats in the saltwater of the Atlantic Ocean doesn’t mean it will float in the constantly moving freshwater of the Mississippi River.

But why does that happen? And what else can we expect to be different when oil spills into a river and not the ocean?

Don’t Be Dense … Blame Density

To answer the first question: When oil floats, it is generally because the oil is less dense than the water it was spilled into. The more salt is dissolved in water, the greater the water’s density. This means that saltwater is denser than freshwater. Very light oils, such as diesel, have low densities and would float in both the salty ocean and freshwater rivers.

However, very heavy oils may sink in a river (but perhaps not on the ocean), which is what happened when an Enbridge pipeline carrying a diluted form of oil from oil sands (tar sands) leaked into Michigan’s flooded Kalamazoo River in 2010. The lighter components of the oil quickly evaporated into the air, leaving the heavier components to drift in the water column and sink to the river bottom. That created a whole slew of new challenges as responders tried new methods of first finding and then cleaning up the difficult-to-access oil.

Going with the Flow

In rivers, going with the flow usually means going downstream. Except when it doesn’t. When might a river’s currents carry spilled oil upstream?

At the mouth of a river, where it meets the ocean, a large incoming tide can enter the river and overwhelm the normal downstream currents. That could potentially carry oil floating on the surface back upstream.

In open areas, such as on the ocean surface, both winds and currents have the potential to direct where spilled oil goes. And along most coasts, wind is what brings spilled oil onto shore.

In rivers, however, the downstream currents usually dominate the overall movement of oil while wind direction often determines which side of the river oil ends up on.

Locks and Other Blocks

Unlike the ocean, rivers sometimes feature structures such as dams, locks, and other barriers that block or slow down the free flow of water. During an oil spill on a river, these structures can also slow down the movement of oil.

That’s a helpful feature for responders who are trying to catch up to and clean up that oil. Frequently, dams and locks cause oil to pool up on the surface next to them. Some of the tools responders use to collect oil from these areas include skimmers, which are devices that remove thin layers of oil from the surface, and sorbent pads and booms, which are large squares and long tubes of special material that absorb oil but not water.

In fact, the banks of the river can constrain spilled oil as well. Because the oil can’t spread as far or thin as in open water, oil slicks can be thicker on rivers, and recovery efforts can be more effective.

One exception is the case of flow-over dams, known as weirs. The water passing over weirs can be very turbulent, causing oil to disperse into the water column. If it is very light oil and there’s not very much, that oil tends not to resurface and form another slick. But sheens may resurface with heavier oils that might be broken up going over a weir but later resurface as the water it is traveling in becomes calmer downstream.

Vegging Out

Oil rings on trees next to a river with boom.

Flooding on the Kalamazoo River in Michigan during the Enbridge pipeline oil spill left a ring of oil around trees and other vegetation after the river returned to its normal level. (NOAA)

Often, plants grow in rivers and line their banks, whereas many parts of the coast are open sandy or rocky beaches, which tend to be easier to clean oil off of than vegetation. (Salt marshes and mangroves being notable oceanic exceptions.) If oil gets past booms, the long floating barriers responders use to prevent the spread of oil, and leaves a coating on plants, then plant cleanup options generally include cutting, burning, treating with chemical shoreline cleaners, or flushing vegetation with low-pressure water.

Plant life actually became an issue during the oil sands spill in Michigan’s Kalamazoo River. Because this river was flooded at the time of the spill and later returned to its normal level, oil on the river surface actually became stranded in tree branches along the riverbanks.

Muddying the Waters

Another issue for oil spills in rivers is sediment. Rivers often carry a lot of sediment in their currents. (How do you think the Mississippi got its nickname “Big Muddy”?) That means when oil droplets drift into the water column of a river, the sediment has the potential to stick to the oil droplets. Eventually (depending on how strong-flowing and full of sediment a river is) some of the oil-sediment combination may settle out to the bottom of the river, usually near the river mouth as the water slows down and reaches the ocean.

One notable example is related to an oil spill that happened on the Mississippi River in New Orleans in 2008. The tanker Tintomara collided with Barge DM932, ripping it in half and releasing all of the heavy fuel oil it was carrying. Downstream of where the responders were cleaning up oil, the Army Corps of Engineers was dredging the sediments that build up at the mouth of the Mississippi and an oily sheen appeared in the collected sediment.

Responders suspected the oil from Barge DM932 had mixed with the river sediment and fell to the bottom further downstream as the river neared the Gulf of Mexico.

Learn more about oil spills in rivers at


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