Is it safe to swim?
Interstate Commission on the Potomac River Basin
Boating, swimming in the Potomac River: How safe is it?
While many do not give it a second thought, others wonder about the safety and cleanliness of the water in the Potomac River and its tributaries. During the summer months, staff at ICPRB field frequent calls from people wanting to know if a favorite spot on their local river or stream is “safe.” With few exceptions, we are unable to provide a definitive answer. The safety can change day-by-day depending on rain, temperature, and other factors. But there are still ways to ensure you have a safe and fun day on the river.
High water levels can cause a normally safe section of the river to have a strong and dangerous current. Carefully inspect the flow before dipping your toes in the water and pay attention to local weather patterns. A storm upstream can create a swift current downstream, causing dangerous swimming conditions. Be aware that currents are generally stronger towards the center of a river and large rocks or rapids can create additional hazards. When the safety of your favorite swimming hole is in doubt, it may be best to skip the swim that day.
Is the Water Clean?
The main concern for water contact recreation (swimming, wading, water skiing) generally is bacterial levels. While bacteria are integral parts of any natural system, some kinds, in sufficient numbers, can cause gastrointestinal illness, skin and ear infections, respiratory illness, and sometimes worse problems. At many areas designated as bathing beaches, or at parks where wading or swimming is officially allowed, water testing is conducted weekly for bacterial contamination. Tests involve examining a water sample for indicator bacteria that signal conditions conducive to the growth of the several types of bacteria that can cause gastrointestinal illness or other infections in people.
Particular areas in which people swim from an uncontrolled beach or from a boat may or may not have a water quality monitoring station in the general area. Many stations are monitored only monthly, and many of those don’t test for bacteria. A typical inquiry to ICPRB asks “I like to water ski with my family downstream of Alexandria, Va. Will we get sick?” Although helpful data is not always available in specific areas, we do provide some general guidance below:
Where does the contamination come from?
In past decades, sewage treatment plants were a major cause of bacterial loads in the river. That isn’t so true any more. Most sewage plants in the region treat to a high degree, and disinfect the water before it is discharged. However, broken sewer pipes that collect waste for transfer to the plant can leak raw sewage into waterways. Heavy rains can cause flows that overwhelm treatment plants. Like any other mechanical device, treatment plants sometimes malfunction and sewage overflows to the river. Additionally, older urban areas, including a large portion of Washington, D.C., are served by combined sewer systems that route sewage and stormwater through the same pipes. Significant rains cause the pipes to back up, and a mixture of sewage and storm water that normally goes to a treatment plant backs up and discharges directly to a waterway or river. This kind of pollution frequently affects the Anacostia River and Rock Creek, and can affect the adjacent segment of the Potomac. Septic systems in rural areas, which are largely unregulated, also can fail or be overloaded by rains.
Other major contaminant sources are mostly related to storm water runoff. Storm water from streets and rooftops of urban and suburban areas carries bacteria-laden trash, pet waste, and other pollutants. In rural areas, agricultural operations can contribute bacteria from animal manure and processing by-products, drugs and chemicals added to feed, sediment, and fertilizer. Beach areas with resident populations of geese and ducks can show elevated bacteria levels. The pace and methods in which land is developed and used can cause bacteria problems in local waterways.
Algae blooms can be harmful, depending on the type. Algae makes up the base of the aquatic food chain, and is essential for healthy waters. When algae grows very rapidly it forms a “bloom” that rises in the water column to form a bright green sheet on the surface. Some algae can be harmful, causing sickness in humans. For more on harmful blue-green algae blooms, visit Maryland Department of the Natural Resources Eyes on the Bay.
In addition to bacteria, traces of many other substances can be found in our waters. The thousands of chemicals in medicines and drugs, personal care products, residential cleaners and pesticides can show up in river water. Some of these substances are known or thought to be endocrine disruption compounds that can interfere with hormonal systems in humans and in the creatures that call the river home. The concentrations may register in the parts-per-billion, and while they may not individually affect an person, the mixture of compounds found in the water has not been studied. Unlike bacterial infections, any possible effects would likely be from chronic (long-term) exposure.
What can you tell us about the safety of my local stream or river?
Bacteria levels can change rapidly with rain events. Except for parks and other facilities where swimming and wading is a sanctioned activity, water monitoring is done at often far-spread stations, usually monthly. Many of these areas are heavily used with no reports of outbreaks of gastrointestinal illness. Without good data, people must decide based on their attitude toward risk and their personal level of health. The odds of a person getting sick increase with the amount of bacteria that enter the body. A small amount is unlikely to affect most people. For that reason, an activity such as boating, where people may just get splashed occasionally, is much less risky than swimming.
If you do choose to swim in the Potomac, here are ways to limit your risk:
- Do not enter the water for several days after a significant rainstorm. Storm flows spike bacteria levels, which decrease with time.
- Do not swallow water.
- Do not enter the water if you have cuts or open sores. These are pathways for bacteria to enter your body.
- Wash after swimming.
- People with immuno-suppressive diseases should avoid direct contact with the river.
- Avoid algae blooms (brightly colored water) and trash in the water.
What about my Dog?
Be extra mindful when allowing your four-legged friend in the river. Dogs can swallow a lot of water while splashing around in the river which increases his or her risk of getting sick. Areas with algae along the surface, where your dog can easily swallow it, should be avoided. Watch the current carefully and keep the dog away from areas that may be too swift for them.
A Swimmable Potomac
If the residents of the basin want a swimmable Potomac–and its tributaries that make up our local streams–both governments and the citizens of the basin will need to make strong commitments to improve water quality. Government agencies tasked with the work will require strong public and monetary support. State and local agencies face competing budget priorities at the same time that land is being developed at a rapid pace. Citizens need to voice their demands for a cleaner environment while becoming stewards of their local waterways. ICPRB promotes stewardship through a variety of outreach and education projects.
People who want to know about bacterial levels in their local waterway should start with their county health department, but the information needed may not exist. Maryland and Virginia host websites that list stations tested for bacteria and their current status, with contacts for some county health departments. For more information, visit or call:
- Office of Environmental Health Services, Dept. of Health and Human Resources – (304)558-2981 or county health departments
Washington, D.C.: Swimming is not an approved activity in the waters of the District of Columbia. Special events, such as triathlons or other competitions that involve water contact require special permits.