Potomac River Sewage Spill: Karen Knee Explains Health and Wildlife Impacts
On January 19, a major sewer line collapse released more than 240 million gallons of raw sewage into the Potomac River, creating one of the largest sewage spills in US history, according to the Potomac Riverkeeper Network. The spill poses serious health risks, threatens local wildlife, and could have lasting ecological and economic effects on the Potomac and Chesapeake Bay ecosystems. Environmental scientist Professor Karen Knee, a faculty member at American University and research affiliate at the Smithsonian Environmental Research Center, explains what’s in the water, what it means for public health and aquatic life, and what the long-term recovery may involve.
What Pollutants Are in the Potomac Sewage Spill and Why Are They Dangerous?
Many kinds of pollutants are in sewage. Two important categories are pathogens (disease causing microorganisms like viruses, bacteria, and parasites) and nutrients (nitrogen, phosphorus, etc.).
Pathogens can make people sick if water enters their mouths, noses, eyes, ears, or open wounds. Usually this would be a GI tract infection or a simple skin infection, but it can include life-threatening flesh-eating bacteria.
Nutrients promote algal blooms, eutrophication (excessive plant and algae growth), and low dissolved oxygen, which can alter ecosystems and threaten aquatic life. Pharmaceuticals and personal care products are also in sewage and can endanger wildlife by being acutely toxic or affecting their endocrine systems (growth, sexual development, etc.).
What Were the Immediate Effects of the Spill on River Life?
Some of the early sampling done by the University of Maryland found that the E. coli levels were about 3,000 times higher than the recreational standard.
The DC District Department of Energy and Environment has also been monitoring bacteria concentrations at different locations in the Potomac. Bacterial concentrations dropped to acceptable levels for recreation by February 2 at the boathouses in the DC neighborhood of Georgetown, but they remained high at Montgomery County’s Swainson Island near the overflow site through February 19.
If a significant number of organisms were killed or harmed by the sewage spill, individual organisms and overall populations may not yet have recovered. Also, once the river warms up, and more light is available, there could be algal blooms, and people who come into contact with the water (while boating, for example) could be exposed to pathogens.
Are Crabs, Oysters, and Other Local Species at Risk from the Potomac Sewage Spill?
None of these creatures benefit from sewage spills. In some cases, the organisms themselves may be okay (or at least not killed off) but they may become unsafe to eat because they absorb the pollution from sewage. This is particularly the case for oysters, which are filter feeders. If pathogens are in the water, oysters can concentrate them and become unsafe to eat.
The biggest threat to the other species would be eutrophication, which reduces the dissolved oxygen to levels where species can’t breathe in the water. Even if this happens for a short time, large fish/aquatic life kills can result.
How Long Will the Potomac River Take to Recover from the Sewage Spill, and What Factors Affect Recovery?
This is one of the largest sewage spills in US history, so it’s hard to say. The water in the Potomac is always flowing downstream into Chesapeake Bay, and it carries the sewage along with it. Imagine dumping some floating trash into the river––it would soon be swept downstream, and after a short time you wouldn’t see the trash at the original location. However, it could cause negative effects when it ends up in the Chesapeake Bay.
However, even once the sewage has been flushed out of the river, there could be lingering effects, such as algal blooms, a decline in populations of fish and other aquatic species, bacteria that remain in the sediment and periodically get re-mobilized, or damage to the river’s perception and reputation that decrease recreation. If species were completely killed off by the spill, that can permanently alter the ecosystem. It’s also possible that the spill could introduce disease organisms that remain in the water, sediment, or wildlife for a long time.
How Do Scientists Track Cleanup and Ecosystem Recovery in the Potomac River?
In a situation like this, you want to track nutrient and fecal indicator bacteria concentrations and the populations of different organisms living in the river (fish, etc.). It would be helpful to have baseline data from before the spill for comparison, so you could see if/when the river returns to pre-spill conditions. Also, you could use data about river flushing and circulation to understand how quickly sewage in the water would be flushed out.
What Lessons Can Be Learned from the Potomac Sewage Spill to Prevent Future Incidents?
If possible, it would be a good idea to increase the frequency of pipe inspections to catch problems before they result in large spills. We have a very old water supply system here in DC, and unfortunately things can fail, so maybe there needs to be more effort into predicting, detecting, and mitigating the effects of those failures.
About Professor Karen Knee
Karen Knee is an environmental scientist whose research explores how human activities—including urbanization, agriculture, and energy development—affect water quality and aquatic ecosystems. Her work has examined groundwater pollution in coastal regions around the world, the impacts of hydraulic fracturing in the Marcellus Shale, and watershed-scale nitrogen cycling. Her current research uses naturally occurring tracers to better understand methane emissions from trees.
She holds a PhD in Geological and Environmental Sciences from Stanford University and an ScB from Brown University. A former Fulbright Scholar in Ecuador, she is a faculty member at American University and a research affiliate at the Smithsonian Environmental Research Center. At AU, she runs the Knee Ecohydrology Lab and teaches courses on water resources, biodiversity, and Earth systems science, and is committed to advancing diversity, equity, and inclusion in environmental science.