Report suggests link between smallmouth bass mortality and water pollution

Citizens urged to advocate for stronger clean water standards

(ANNAPOLIS, MD)—Scientists suggest that a perfect storm of pollution, parasites, warming water temperatures, and endocrine disrupting chemicals may be combining to threaten one of the region's most popular fresh water game fish, the smallmouth bass, according to a new Chesapeake Bay Foundation (CBF) report. In Virginia, recreational anglers targeting smallmouth bass contribute $341 million to local economies, supporting 2,200 jobs, according to data from the American Sportfishing Association and the U.S. Fish and Wildlife Service.

"Smallmouth bass are one of the most prized game fish," said CBF President Will Baker. "While the current problems are primarily in Pennsylvania, over the last decade we have seen how vulnerable the population is in Virginia, with fish kills in the Shenandoah and Cowpasture rivers."

Since those kills, the smallmouth bass population has rebounded in the Shenandoah, but the population in the Cowpasture is unclear because of insufficient monitoring.

The reasons for the Shenandoah's rebound are not clear. Pollution has been reduced, and favorable spring rains may have helped the survival of juvenile fish. But the Shenandoah is still in trouble. Large algae blooms, fed by nitrogen and phosphorus pollution smother the river at times during hot months.

This spring Department of Environmental Quality (DEQ) will be reviewing Virginia's water quality standards. CBF believes that new standards for nitrogen and phosphorus pollution in freshwater streams, based on sound science, are needed to protect aquatic life and recreational uses. CBF encourages citizens who care about clean water to let DEQ know of their concerns.

CBF's report, Angling for Healthier Rivers, shows the possible link between phosphorus and nitrogen pollution and diseased and dying smallmouth bass. It also found that:

  • Scientists believe that nitrogen and phosphorus pollution may be contributing to the fish deaths and diseases in two ways. The first is by spurring the growth of parasites (myxozoans and trematoads) and their hosts (worms and snails). The second is by feeding algal blooms that raise pH levels and lower oxygen concentrations, stressing young smallmouth bass.
  • In the Susquehanna River, anglers first reported diseased and dying smallmouth bass in 2005. Since that time, catch rates are now a mere 20 percent of what they were before. The situation has become so serious that, to reduce stress on spawning fish, the Pennsylvania Fish and Boat Commission is halting all fishing for smallmouth bass from May 1 until June 15, for the second year in a row. Many fisheries scientists fear a collapse of the smallmouth bass fishery there. 
  • Between 82 and 100 percent of male smallmouth bass in the Potomac and Shenandoah rivers have sexual abnormalities. Scientists have also found intersex fish in the Susquehanna River, where between 89 and 93 percent of the male fish sampled had sexual abnormalities. The cause remains unknown, however a recent study found 135 different chemicals in the water over smallmouth bass nesting sites.

Smallmouth bass do not tolerate pollution well. In fact, some suggest that smallmouth bass may be like a canary in the coal mine indicating future possible health problems for other species of fish. High levels of nitrogen and phosphorus pollution, rising water temperatures, and endocrine disrupting chemicals may all have combined to weaken the immune systems of smallmouth bass and make them more susceptible to naturally occurring bacteria, viruses, and parasites.

"It's almost like you reach a perfect storm situation," said Dr. Vicki Blazer, Research Fisheries Biologists for the U.S. Geological Service, and a lead researcher of the smallmouth bass. "There have been stressors and smallmouth bass have been able to overcome them or deal with them. But eventually, they get to a point where they cannot deal with them anymore."

Virginia's Clean Water Blueprint lays out the steps that need to be taken to reduce pollution and improve water quality in local rivers, streams, and the Chesapeake Bay. CBF encourages the Commonwealth to aggressively implement the plans it has developed.

Read the report

Decades of Success: The 1970s

Even as a young organization, our work was effective and got noticed. Find out what we did.

Explore Our Timeline


Do you enjoy working with others to help clean the Chesapeake Bay? Do you have a few hours to spare? Whether growing oysters, planting trees, or helping in our offices, there are plenty of ways you can contribute.

This website uses cookies to tailor and enhance your online experience. By continuing, you are agreeing to our use of cookies. For more information, including details on how to disable cookies, please visit our Privacy Policy. Agree