Fish in the Anacostia River have cancerous tumor rates that are as high as ever documented in an American river, and a U.S. government-led study to be published next month links the tumors to pollution caused by vehicle emissions and runoff.

Fifty to 68 percent of mature brown bullhead catfish collected in 2001 from three parts of the river in the city had liver tumors, most of which were cancerous, according to the study led by the U.S. Fish and Wildlife Service. In addition to the liver tumors, 13 to 23 percent of the bullheads had skin tumors, scientists found.

"It says that there are serious problems with the health of the fish and that it's a highly polluted system that needs a lot of work," said Fred Pinkney, co-author of the study and a scientist in the Chesapeake Bay field office of the Fish and Wildlife Service.

The study, scheduled for publication in the March issue of the scientific journal Environmental Toxicology and Chemistry, links the liver tumors to changes in the DNA of the fish. Those DNA changes were, in turn, linked to polynuclear aromatic hydrocarbons (PAH) -- contaminants that often come from fossil fuels, most commonly in the form of settled vehicle emissions and runoff.

Bullhead catfish have been analyzed by scientists as an indicator of the health of river systems for decades, mainly because the fish are bottom-feeders and burrow into the mud during the winter, increasing their exposure to sediment pollution. According to the study, scientists' rule of thumb is that liver tumor rates exceeding 5 percent qualify an area as "highly contaminated."

This isn't the first time the tumor rates in the Anacostia have been surveyed, and it's not the first time the results have been the cause for concern. A 1996 study of Anacostia fish, also organized by Pinkney, cited liver tumor rates ranging from 50 to 60 percent. After that study was published, the environmental advocacy group American Rivers deemed the Anacostia the nation's most polluted river.

The study comes at a time when many people have high hopes for the Anacostia. The river, with tributaries beginning in Maryland, flows into the Potomac River and empties into the Chesapeake Bay. An estimated 90 percent of its banks are developed, which means rainwater often runs over concrete and into the river without being filtered by soft ground or vegetation. Many types of PAH contaminants, therefore, can end up in the river -- vehicle emissions that have settled on the ground, engine oil, even carcinogenic particles contained in asphalt.

"The Anacostia is kind of like a sink for what people throw in the street," said Nick DiNardo, an Environmental Protection Agency manager who oversees projects for the Anacostia Watershed Toxics Alliance, a partnership of 28 agencies and jurisdictions formed in 1999 to spearhead restoration efforts.

And the fish study suggests that sink is one of the dirtiest in the nation. John C. Harshbarger, a pathologist with George Washington University Medical Center who analyzed the tumors, said the slightly higher numbers found in the recent study suggest that the liver tumor prevalence in the Anacostia is equal to that in Ohio's Black River in the early 1980s, a river that was considered highly polluted by a coal coking plant. The Black River rates, which averaged roughly 60 percent, have been considered the highest ever found, Harshbarger said.

"When they closed the coking plant on the Black River in 1982, five years later, the PAH levels in the sediment plummeted, and fish cancer rates really dropped, too," he said. "In the Anacostia, there hasn't been one source you can point to to close down and let the river remediate itself. I'd say whatever was causing the tumors in 1996 is still there."

State and federal groups have targeted the river for cleanup efforts for years. The Anacostia Watershed Toxics Alliance has identified more than 700 projects, including efforts to restore wetlands, reduce sewage overflow and retrofit stormwater systems.

Plans to reduce sewage emissions have received a lot of attention, partly because such efforts are expensive. Much of the D.C. sewer system uses the same pipes for sewage and stormwater, which can dump sewage into the river during heavy rainstorms. The city has a plan to replace those lines at an estimated cost of $1.35 billion, though it has been only partially funded.

The city wants the Anacostia riverfront to become a model of urban redevelopment, and it recently announced an $8 billion plan to upgrade the riverfront. The plan includes an environmental overhaul involving the creation of more wetlands and riverfront parkland, which could help stop polluted runoff from flowing into the river, according to Uwe Brandes, a project manager for the Anacostia Waterfront Initiative with the D.C. Office of Planning.

"What's unusual about the revitalization of the river in this case is that there are a number of sites along the river that today impact it in a negative way," Brandes said. "The redevelopment of those areas will help rebuild the public infrastructure there that's needed to control storm runoff."

The EPA's DiNardo warned that the tumor study should not be considered the sole indicator of the river's health. He said the Anacostia Watershed Toxics Alliance is working to collect data that will help determine the progress made through ongoing projects.

"We need to establish a base line so we can gauge whether things are getting better or not based on a wide range of indicators," he said. "That hasn't been done yet."

But some said the tumor study, which was provided to The Washington Post by the nonprofit group Natural Resources News Service, indicates that the ongoing efforts, such as sewage overflow reductions, aren't enough. Robert Boone, who founded the Anacostia Watershed Society in 1989, said the link to fossil fuel pollution suggests that current cleanup efforts might be overlooking the primary source of the problem.

"We're slated to get another million people in the area in the next decade, and they'll all need a car," he said. Stopping sewage overflows and creating new wetlands "is a noble effort and needs to be done, but it's a Band-Aid on a hemorrhage. The problem is pollution from vehicles," he added.

The D.C. Department of Health has discouraged anything other than catch-and-release fishing in the Anacostia since the late 1980s and advises people not to eat bottom-dwelling fish.