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Intersex Bass Turning Up on the Susquehanna, Potomac, and Shenandoah Rivers

Contaminants in these Chesapeake Bay tributaries have crippled the smallmouth fisheries.

Intersex Bass Turning Up on the Susquehanna, Potomac, and Shenandoah Rivers

At some locations on the Susquehanna River, up to 100 percent of the male smallmouth are producing eggs in their testes—a condition known as intersex—and gooey blue-green algae blooms are choking the oxygen out of the water. (Jay Nichols photo)

When fly fisher Brian Shumaker began guiding on the Susquehanna River 23 years ago, it was considered one of the best smallmouth bass fisheries in America. Since the young-of-year crash of 2005, though, Susquehanna smallmouths have suffered periodic mortality, viral and bacterial infections, parasite infestation, and habitat woes.

“We get these shore-to-shore algae blooms that leave the rocks with a strange residue,” Shumaker says. “We lost our grass beds in a hurricane 10 years ago and they haven’t come back.”

It’s a similar story on the Potomac River and other Chesapeake Bay tributaries, where disease and episodic die-offs have plagued mostly adult smallmouths. Former fly-fishing guide Jeff Kelble, now president of Potomac Riverkeeper (, described “epic blooms of gooey blue-green algae” when he served as Shenandoah Riverkeeper until July.

What is even more disturbing to some is that on all of the bay’s major rivers, otherwise healthy male smallmouths—up to 100 percent of them in places—are producing eggs in their testes, a condition known as intersex that appears to be impacting reproduction.

“That’s where it gets really scary,” says Upper Potomac River manager Brent Walls. “Something very acute is affecting bass at a genetic level. You’ve got to wonder, if it’s having this effect on little guys in the river, what is it doing to us?”

Although the rivers’ problems have confounded scientists for a decade, they are piecing together a puzzle they expect will reveal a variety of culprits from farm runoff and human waste, including pharmaceuticals and other products we use in our everyday lives, such as plastic water bottles, weed killer, hand sanitizer, plastic garbage bags, and toothpaste.

“People want one smoking gun, but I think we’re going to find many,” says Vicki Blazer, a fisheries biologist with the U.S. Geological Survey, who discovered the intersex phenomenon on the South Branch of the Potomac while investigating a bass die-off there in 2003. “My gut tells me we’re dealing with a complex mixture of contaminants that are inducing both poor immune response and intersex fish.”

Blazer and her team are matching tissue samples of sick and intersex bass with river conditions during the years they were hatched. They also are analyzing contaminants in bass eggs harvested last year and in water and sediment samples. More samples will be collected this year.

Bass survival and evidence of disease vary with conditions and the cyclical nature of fisheries, Blazer says. “In high-flow years, you expect more pollutants from agricultural runoff, as well as poor recruitment from nesting fish. When rivers are low and warm there is less dilution of pathogens from point sources, like wastewater treatment plants.”

Ferreting out the contaminants that get piped or washed into waterways is a daunting challenge, given their vast number.

Of particular interest are estrogenic compounds, including naturally occurring estrogens excreted by people, livestock, and other animals, and those created in labs that have similar effects. “They’re endocrine disruptors. They interfere with an animal’s hormone system,” says Blazer. “And they exist in thousands of things that may surprise you, like plastics, pharmaceuticals, and personal care products.”

Known as contaminants of emerging concern, some are just now being studied by federal and state environmentalists but are largely unregulated in terms of their impact on rivers that supply drinking water and sustain aquatic life.


The Environmental Protection Agency only regulates for nutrients and human pathogens, such as E. coli, but not for other compounds, including pharmaceuticals, that may be just as harmful, says Blazer. “Some may be removed incidentally by wastewater treatment plants, but they aren’t required to remove them, and the chemistry they use hasn’t kept up with the number of products entering our waterways.”

Many do not break down in the natural environment, according to Gary Ankley, a research scientist with the EPA in Duluth, Minnesota. “Even compounds in low concentrations can produce biological effects on wildlife.”

For instance, studies by University of Wisconsin-Milwaukee researchers indicate that Prozac and other antidepressants—among the most commonly prescribed medications in America—lowered the sex drive of male minnows and caused females to produce fewer eggs. Other research indicates these same drugs disrupt the reproductive cycle of mussels, which filter toxins from water at the base of a fishery’s food chain.

“Prozac could accumulate in the brains of bass, making them less aggressive about guarding their nests,” Blazer says.

One of the more pervasive endocrine disruptors on the Potomac and Susquehanna is triclosan—an antimicrobial commonly found in hand sanitizers as well as other items such as toys and mouthwash—that just now is being scrutinized by the Food and Drug Administration for potential harmful effects on humans.

Intersex Smallmouth Bass Turning Up on the Susquehanna, Potomac, and Shenandoah Rivers
Fisheries biologist aides Aiden Simpson and Scott Bennett sample the Susquehanna River near the mouth of Conodoguinet Creek, for smallmouth bass. (Photo courtesy of the Pennsylvania Boat and Fish Commission)

“We see it again and again accumulating in the skin of fish,” says Blazer. “The mucous covering on their skin is their first defense against bacteria and parasites; it contains a normal flora that is protective in some ways. So my question is, ‘What are these antimicrobials doing to that normal flora?’ Perhaps impacting the skin lesions we’re seeing.”

In rural hot spots on the Susquehanna and Shenandoah, farms are packing a double wallop, by loading water with nutrients that feed bacteria and by adding chemicals used in agricultural production, says Blazer.

“When fish have low immune response, a high phosphorus and nitrogen load opens the door for them to become ill from pathogens that are otherwise fairly innocuous. The natural hormones and testosterones in manure, as well as those that mimic estrogen in herbicides and pesticides, are a big influence on intersex . . . bigger than effluent from wastewater treatment plants.”

Atrazine—which is banned in Europe but remains the most commonly used weed killer in the U.S.—is of particular concern. Cheap and effective at no-till production of low-margin crops such as corn, it is suspected of causing harm to human reproductive and immune systems.

“It’s another compound that keeps showing up in our studies,” says Blazer, who links it to feminized male bass. “If a herbicide kills a lot of plants, which have high concentrations of phytoestrogens and they get into the water, it will add to estrogenic levels, which could relate indirectly to intersex fish.”

Scientists aren’t certain when intersex develops, but suspect it is induced from birth and increases in severity with exposure to pollutants over a lifetime. “We think mothers pass contaminants to their spawn in the sac fry stage, when they feed on yolk in the first two or three weeks of life,” says Geoff Smith, the Susquehanna River biologist for the Pennsylvania Fish & Boat Commission (PFBC). “But eggs deposited in redds also may be absorbing chemicals through sediment. We don’t yet know the break point.”

Whatever researchers ultimately determine about the rivers and their fisheries, it will be up to politicians and policy makers to ensure problems get fixed, says Smith. “And that will be a whole other story.”

Despite pressure from the PFBC and environmental groups such as the Chesapeake Bay Foundation, the Pennsylvania Department of Environmental Protection has so far refused to designate the main stem of the Susquehanna as impaired, a listing that would go a long way toward bringing agricultural pollution under control.

And while portions of the Potomac and Shenandoah have impaired status because of bacteria content, Virginia refused in late October to list the Shenandoah for lost recreational and aesthetic value because of algae, and the EPA, citing insufficient data, declined to intervene.

The EPA also has refused to over-rule the Pennsylvania DEP on the Susquehanna’s status, but, at the urging of PFBC Executive Director John Arway, agreed in recent months to lead the river’s stakeholders in reaching consensus on the river’s status by late in 2015, Arway says.

“They offered to volunteer staff to bring together all of the information we’ve collected, from the state, the USGS, university academics, the Susquehanna River Basin, and process it through the CADDIS (Causal Analysis/Diagnosis Decision Information System) website,” Arway says, in reference to a Web-based resource for assessing rivers.

“It will be a collaborative effort, and I’m happy we’re finally on the path for an answer.”

In another vein, the EPA is also working with all Chesapeake Bay states on a bay cleanup plan aimed at having pollution controls in place by 2025. At the same time, major cities on the bay are under federal orders to upgrade municipal sewer systems so that raw waste no longer will get piped directly into rivers during major storm events, and treatment plants can process larger loads.

But such changes will take years if not decades to implement, may not cover emerging contaminants, and will require the commitment of every stakeholder in the watershed to succeed, says Liz Deardorff, a director at American Rivers, an advocacy group that named the Susquehanna, the Potomac, and the Shenandoah as among the most endangered rivers in the U.S. in recent years.

“All of the pieces have to come together,” Deardorff says. “But the EPA is answerable to legislators, and there’s pushback from entities like the farm lobby that worry about too much regulation. Everybody has a complaint in a different direction. It’s a natural part of the process.”

In the meantime, public education is critical, so individuals can make simple lifestyle changes that are healthier for them and for the rivers, Blazer says. “Organizations like Audubon or even Girl Scouts can help people understand how what we use affects the environment…how we can make a difference by buying fragrance-free laundry detergent, hand sanitizer made with alcohol, not triclosan, and by putting fewer chemicals on our lawns.”

Blazer uses a water purifier at home and carries water in a metal container.

“You think you’re doing a good thing by buying bottled water, but unless you’re drinking from a bottle that is BPA-free, you’re ingesting compounds from the plastic, and once you excrete them, they are winding up in rivers, untreated,” she says.

“What’s even worse is that all of those plastic bottles are winding up in landfills, and leaching into groundwater that goes into our rivers.”

Deborah Weisberg is an award-winning journalist whose work appears in the Pittsburgh Tribune-Review, The New York Times, BASS Times, and Pennsylvania Outdoor News. She lives in Pittsburgh, Pennsylvania and is a frequent contributor to Fly Fisherman.

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