The specifics are murky but the problem is clear: Toxic chemicals in the Anacostia River are invading the food chain from the bottom up, all the way to the people who live along its shores.

Research has shown that fish and clams in the river absorb toxins that lie in the river bottom and move through the water column. When people eat the fish, they eat toxins too.

A new study by a coalition of organizations, including the Anacostia Riverkeeper, has found that many people fish the Anacostia not just for fun, but for food. The findings will be detailed in an upcoming report called "Addressing the Risk."

"We were surprised by the amount of fish consumption going on," said one of the report's authors, Steve Rabbe, president of the research company OpinionWorks. "It's really permeating the surrounding neighborhoods and reaching vulnerable people like children, pregnant women and the elderly."

The Anacostia is one of the nation's most polluted rivers. Its course runs through a heavily developed watershed that begins in Maryland headwaters, travels through the District of Columbia and merges with the Potomac River a few blocks from Capitol Hill.

The Anacostia's problems are well-known, and toxics aren't the only items on the list. The river is also plagued with trash, bacteria, nutrients and sediment, much of which is carried by the violent rush of stormwater from the hard urban surface.

Toxins are the culprit, though, in a study of brown bullhead catfish in the Anacostia River. The U.S. Fish and Wildlife Service found that 50–68 percent of the fish had liver tumors and 10–23 percent had skin tumors.

Harriette Phelps, professor emeritus with the University of the District of Columbia, has spent 12 years mapping toxic problems in the Anacostia by analyzing the level of contaminants in clam tissue.

Phelps found high levels of contaminants at each of her 45 monitoring sites. Polycyclic aromatic hydrocarbons were the greatest and most widespread contaminant. PAHs are chemicals produced by combustion, including automobiles and power generation. Some cause cancer.

High PAH levels in five Anacostia tributaries appeared to originate at upstream industrial parks and metro stations. Chlordane was the most common pesticide found, and its levels exceeded the federal action level for human fish consumption in four upstream tributaries.

Phelps is anxious for action. "Scientists are aware of this but the politicians are not dealing with it," she said. "There are solutions."

For decades, the Anacostia's problems piled up and stagnated. It was called the "forgotten river," and the people living along its shores — in a disproportionate number of minority and low-income neighborhoods —likely felt forgotten, too.

But the Anacostia is now drawing more attention from community groups, conservation organizations, government agencies and developers who aim to improve both the river and quality of life for its communities.

As a result, the baffling challenge of toxic contamination in the river is receiving slow but strategic action.

Fixing the problems depends on understanding them, and both steps are complicated.

Some toxic substances have been bound to sediment in and along the river for decades, the legacy of industrial and military activity that occurred before stricter environmental regulations were in place. Modern sources also exist — some are site-specific. But some contaminants, like PAHs and pesticides, come from the accumulation of chemicals spread widely across the landscape.

The Anacostia is also a muddy river, thick with sediment scoured from its banks by the violent rush of stormwater from streets, rooftops and parking lots, as well as bottom particles disturbed by dredging. This means that toxics both old and new are often on the move. Proving their point of origin can be tricky.

Research on problems and sources has been under way for more than a decade. In 1999, the EPA organized a group of 25 organizations into the Anacostia Watershed Toxics Alliance. They studied bottom sediment in the lower, tidal portion of the river and produced a map of hot spots and led discussions on next steps.

The alliance has not been active recently. But the District of Columbia's Department of the Environment (DDOE) has spent the last few years using its findings to broker cleanup agreements with PEPCO and Washington Gas, property owners near two of the identified hot spots.

DDOE also collected penalties from transportation company CSX for a coal spill and arranged for CSX to clean up shoreline property adjacent to their rail yard.

The National Park Service is evaluating cleanup strategies for Kenilworth Park, which was created on an unlined landfill before it came into federal hands.

The DDOE, EPA, and U.S. Navy are involved in a long and complex cleanup of contaminants at the Navy Yard directly on the shores of the river.

Paul Conner of the DDOE called such projects progress, but said they won't be enough.

"If you look at these individual parcels, they make progress, and that's a great thing," Conner said. "But they look at sediment along their piece of the shoreline. There is not a project that looks at sediment as whole and, in particular, no effort until recently to look at the sediment in the middle of the river. We've just launched a project to do that."

The District will spend $1.5 million in fiscal year 2013 to launch the multi-year project, which may lead to a more aggressive cleanup.

Brooke DeRenzis, project director with the nonprofit organization DC Appleseed, said that he hopes the study will lay the groundwork for an enforceable, holistic approach under the federal Superfund law for hazardous areas.

"We need to approach the tidal estuary as a whole because the sediment moves around with the tides," DeRenzis said. "Under the Superfund law, we could look at the tidal portion of the river as a whole unit."

But solutions must also address problems in the nontidal headwaters.

By placing clams in small cages at various locations in the watershed and measuring the amount of toxins in their tissue, Phelps has worked steadily upstream, tracking problems to origins across the Maryland border.

Phelps said that she believes these upstream contaminants are washing into tidal areas near Bladensburg and on toward the District of Columbia. She argues that tackling specific, upstream sources could reduce toxics more quickly and more cost-effectively than a widespread effort to reduce the volume and speed of stormwater.

The Maryland Department of the Environment has conducted follow-up studies of Sligo Creek, where Phelps found high levels of chlordane, and Lower Beaver Dam Creek, which proved high in polychlorinated biphenyls (PCBs).

MDE confirmed the PCB problem in Lower Beaver Dam Creek and is working to pinpoint the source. Additional studies of fish tissue in Sligo Creek did not show levels of chlordane high enough to trigger a fish advisory.

"But it's still an open issue," said MDE toxics specialist Leonard Schugam. "If contaminants are being picked up by sediment and washing downstream, is it contributing to issues down there?"

At DDOE, Conner hopes that the new study will shed further light on whether or not significant amounts of toxins are transported from upstream to downstream in what he calls a "train of contaminated sediment."

If the District's research delivers on its promise to characterize the river — and strengthens cooperation between the federal government, District of Columbia and Maryland — the Anacostia might finally serve up fish that pose less risk to the people who consume them. But such results are likely years away and, so far, there have been far more studies than action.

"Lots of people fish here, and they eat the fish," Phelps said. "Attention needs to be paid."