Learn what threats are facing local fish populations

Fishing in the Potomac River — Photo by potomac conservancy

You might have seen the up-grade the Potomac River has gotten from a team of experts that judge the river’s health—jumping from a B- to a B in the past 3 years.

While it’s true the river’s getting better thanks to the tireless work of many community partners, that doesn’t mean you can dive in headfirst or enjoy a meal out of a freshly caught striped bass from the river.

Due to public health concerns, it is currently illegal to swim in the Potomac River and eat its fish in and around Washington, DC.

As inhabitants of the Potomac, fish have more firsthand experience with the river than most of us, making them one of the key indicators of the river’s health. Paying attention to their population sizes and physical health is crucial in understanding what work remains to be done in the fight for clean water.

Spearheading further restoration and conservation efforts, our goal is to make sure the entire Potomac River is swimmable and fishable for everyone.

photo by brendan ross via flickr (CC BY-SA 2.0)

The fish from the Potomac River and its tributary streams have fed local communities for centuries. Native peoples invented new ways of harvesting fish to support their tribes, relying on the Potomac for food as well as a source of livelihood as they used the river for a trading route.

Today, many people in the region still incorporate fish into their everyday diets, but pollution, a changing climate, and other environmental factors are making them unsafe for human consumption. They’re also hindering some fish species’ ability to reproduce.

So what exactly makes the fish in the Potomac not safe to eat?

We already know that the health of a river is directly linked to the health of its fish. Clean water supports thriving fish populations, whereas polluted waters cause them to struggle.

Some fish in the Potomac River are still dealing with the effects of legacy pollutants such as acid drainage from coal mining that polluted the river in the late 20th century. Striped bass is one species that continues to suffer from legacy pollution, making it particularly unsafe to eat when found in waters around Washington, DC.

Other pollutants harm fish as well, some even having hormonal effects. Toxins like heavy metals and polychlorinated biphenyls, or PCBs, have been linked to cancer and negative effects on the immune, reproductive, nervous, and endocrine systems in both fish and people.

Research has found that immune systems of smallmouth bass suffer from pharmaceuticals dumped in sewage, as well as chemicals from fertilizers, pesticides, and herbicides.

smallmouth bass. Photo by pverdonk via flicker (CC BY-NC 2.0)

But pollution is not the only challenge fish face.

As is usually the case with environmental concerns, there’s not one clear culprit responsible for poor fish health. It’s multiple factors simultaneously impacting the aquatic creatures.

One of the factors harming local fish populations is the warming climate. A key indicator species of the Potomac River’s health, brook trout (known as “speckled trout” or “brookies”) is especially sensitive to temperature changes and requires a stream temperature of about 65°F to thrive.

Dwindling streamside forests does not help the matter, as one of the principal benefits of trees is shade, making sure temperatures don’t get too high for these chill fish.

The only trout species indigenous to Maryland, Virginia, and West Virginia, brook trout are currently threatened by rising temperatures, highlighting the need for land conservation along the river’s shores.

Shade is just one of many benefits that trees offer, though. Without an adequate defense provided by forested lands and streamside trees, there’s nothing stopping rainwater from picking up pollutants and entering the river, introducing harmful chemicals and increasing sediment levels.

A bountiful tree canopy, with abundant roots underground, works to keep water from entering the river on two levels. The leaves and branches intercept rain directly from the sky, reducing the amount of water that makes it to the ground. Meanwhile, the roots absorb and filter stormwater, which mitigates flooding and prevents sediment and other pollutants from infiltrating waterways.

This is especially important as polluted, murky waters can throw the river ecosystem off balance. Aquatic vegetation—such as underwater grasses—that fish rely on for food and shelter struggles to grow in turbid water, and it can also lead to increased amounts of algae blooms and decreased levels of oxygen.

The Potomac River still experiences sediment pollution, though it is slowly improving. Despite this, many fish are sensitive to unclear waters. Smallmouth bass provide one example of how muddy waters can negatively impact fish throughout the river, with these bass failing to grow their populations in the past decade.

Decreasing sediment levels and restoring underwater grasses is necessary to improve not only the health of smallmouth bass but many other species that require clear waters and plentiful amounts of vegetation.

Aquatic vegetation. photo by Will Parson/Chesapeake Bay Program

Invasive fish threaten locally evolved fish populations, too.

Another threat to native fish is the presence of species that did not evolve locally, such as the blue catfish and snakehead. As part of an effort to control blue catfish populations, the Maryland Department of Agriculture spends $30,000 each year to drive up commercial demand for the invasive fish. However, experts say that more will need to be done to keep their populations in check.

Commercial anglers in Maryland and Virginia have seen an increased demand for blue catfish, though, and have informally stated that the species has become trickier to find in recent years.

Other potential mitigation strategies include creating commercial fisheries for blue catfish as well as establishing coordinated and consistent monitoring across states. The Chesapeake Bay Program is working on implementing effective methods to curb these populations.

As a sought-after prize in some fishing spots, snakeheads present an enjoyable challenge for anglers. The U.S. Fish and Wildlife Service encourages fishing for this non-native species, noting that anglers can remove over 25% of the snakehead populations in their local areas.

So if you’re an angler, consider tackling these problem fish head-on by targeting snakeheads or blue catfish on your next fishing trip!

A beacon of hope

It’s not all bad news though. Shad populations continue to thrive in the Potomac River, after many years of restoration efforts.

While other rivers in the Chesapeake Bay watershed are still experiencing difficulties in shad populations, their continued success in the Potomac serves as a beacon of hope. Restoring shad populations is one attainable goal to work towards in the Potomac and other regional waterways.

🐟 So, now you’re in the know about the Potomac River’s fish! That said, they’re just one important indicator of the river’s overall health.

Check out our most recent Potomac report card to see how our hometown river’s health is improving and what work still needs to be done to make it safe and clean for everyone in our community.

read the report card