A fisherman holds a smallmouth bass with cancer caught in the Susquehanna River. (R. Bane/Pennsylvania Fish and Boat Commission)

Smallmouth bass that draw hundreds of millions of dollars to the Chesapeake Bay region for sport fishing are sick, and many look too awful to ever mount as a trophy.

A report released Thursday by the Chesapeake Bay Foundation says the fish, particularly those in the lower Susquehanna River, have been struck by a perfect storm of pollution, parasites, disease and endocrine disruptors that are changing the sex of males.

The catch rates of adult bass fell 80 percent between 2001 and 2005 in some areas of the Susquehanna River, the report said, citing a study by the Pennsylvania Fish and Boat Commission.

The director of the commission, John Arway, said Thursday that he caught and released 200 bass on a summer night before 2005 and can now catch only three or four. Arway said that anglers who come up empty-handed are shying away from the smallmouth bass, valued at nearly $650 million in 2011, according to the American Sportfishing Association.

The foundation is calling on the Environmental Protection Agency to designate a 98-mile stretch of the river as “impaired” under the federal Clean Water Act, “and a decision is due any day,” said William Baker, the foundation’s president. If the EPA makes the designation, Pennsylvania could be forced to require farms and cities to limit nitrogen and phosphorous pollution that runs into the bay more aggressively than the current cleanup plan that is set to run until 2025.

The Pennsylvania Department of Environmental Protection has said an impaired designation is premature. It said that baby smallmouth bass succumb to disease in some of Pennsylvania’s most pristine waters, a mystery that requires more study. “We don’t make impairment designations based on the health of a species of fish. We make them based on water quality,” said Kevin Sunday, a department spokesman.

Baker called smallmouth bass a “canary in the coal mine” because the fish is sensitive to pollution, and what harms that fish could later affect others. “This report and its findings must not be ignored,” Baker said.

In a bit of good news from an unrelated study released this week, the U.S. Fish and Wildlife Service said bullhead catfish in the Anacostia River were found to have about half as many cancerous liver tumors and skin lesions than when a similar survey was completed in 2001. It attributes the decline to efforts to decrease pollution in the Anacostia.

“I think it shows the trend is going downward, and with continued actions it will continue to go lower,” said Fred Pinkney, a Fish and Wildlife biologist.

Despite the improvement, bullheads from the Anacostia and several Potomac watershed locations still have liver tumor prevalence significantly higher than the bay-wide estimate for cancer, the study said.

Bullhead catfish are one of several species of catfish in the river that runs through the District and Maryland suburbs. Cancer is so prevalent that local health departments strongly discourage eating catfish from the river.

Smallmouth bass are troubled throughout the watershed. In addition to the Susquehanna, fish with lesions were found in the north and south branches of the Shenandoah River, the south branch of the Potomac River, the Monocacy River and the Cowpasture River.

The Maryland General Assembly recently passed a bill that requires farmers to report the exact amounts of insecticides used to treat their fields. Biologists fear that pesticides, mixed with hormones from human pharmaceuticals in urban wastewater that pours into rivers, are causing male bass to develop eggs in their testes, switching sex.

Arway said the evidence is clear. “We’ve found black spots on adult fish, exotic viruses, parasites and invasive species . . . some of which we’ve never seen in our waters before,” he said. “We can’t wait to research when our final bass dies.”