The city's three main waterways are heavily contaminated with sewage bacteria at levels routinely more than 10 times what is considered safe for public health, and sometimes 100 times the safe level.
Environmental experts agree that chronic leaks and undetected breaks in the city's aging, deteriorated sewer lines are probably responsible for most of the contamination in Herring Run, Gwynns Falls and Jones Falls.
A top Environmental Protection Agency official said the situation apparently violates the federal Clean Water Act, the nation's premier water pollution law, which leaves polluters vulnerable to fines of up to $27,500 each day the pollution persists.
More than 90 percent of the monthly tests done on all three streams, which flow through heavily used public parks, show high levels of bacteria at nearly all of the stations tested, said Bill Stack, chief of the Department of Public Works office responsible for monitoring the streams.
Bacteria levels "far exceed the state standards, quite a lot," Stack said. "The data hasn't shown there to be any improvements" since the monitoring began in the early 1990s.
City Health Department tests last fall also found widespread fecal coliform contamination in most city streams, Health Commissioner Peter Beilenson said. And the Herring Run Watershed Association, an environmental group, has gotten similar results over several months' worth of testing along that stream.
The contamination poses two problems: It exposes people who splash in the streams to the risk of intestinal disease, though health officials say that risk is hard to determine. "In terms of overall environmental hazards ... I would place it in the middle range," Beilenson said.
And it adds to the environmental degradation of downstream waters, including the Chesapeake Bay - though again, experts say that since the amount of sewage leaking into the streams is unknown, the impact on the bay can't be measured.
"The regulatory situation is pretty straightforward," said Michael Cook, director of the Office of Wastewater Management at EPA headquarters in Washington. "We would consider that kind of leak an unpermitted and illegal discharge ... an enforcement action could be taken."
Cook said the responsibility for enforcing the law rests with the Maryland Department of the Environment. "They should be taking the lead authority for making sure that Baltimore gets the job done," he said.
MDE officials said they could not comment about the agency's Clean Water Act enforcement efforts because it would jeopardize negotiations with the Department of Public Works.
"We are working with Baltimore City to address corrective actions in their failing infrastructure systems," said John Verrico, an MDE spokesman.
But Ralph Cullison, chief of the DPW's environmental services division, said negotiations with the MDE involve a different set of problems with the city sewer system. Cullison and other DPW officials said the MDE has not put any pressure on the city to clean up the contaminated streams.
Jaswant Dhupar, the DPW's chief of water and wastewater engineering, said the department undertook on its own initiative a $194.5 million program to replace and repair failing sewer lines and equipment. About $135 million of that will go to projects that should eventually improve water quality in the three streams. Those jobs will take five to 15 years to complete, Dhupar said.
Meanwhile, a Health Department effort to post warning signs along the three streams, and other contaminated city waters, was delayed for several months by a shortage of signs and by miscommunication.
"I think something sort of dropped there for a couple of months," Beilenson said yesterday, pledging that the signs will be posted along heavily contaminated city streams "over the next two weeks."
Beilenson stressed that the stream contamination has no effect on the city's water supply, which is safe to drink. Stream water tainted with the bacteria can make people sick if it gets in their mouths - for example, when they touch their lips with wet hands.
Local environmentalists said they have been trying to get city, state and federal authorities to crack down on the problem, with little success.
"These streams are flowing through our neighborhoods, and they're degrading the parks and the quality of life," said Richard S. Hersey, executive director of the Herring Run Watershed Association. "The government officials don't seem to have the sense of urgency we think is appropriate."
Using a $35,000 grant from the EPA, the Herring Run Watershed Association has been monitoring the stream - testing for fecal coliform, looking for leaks and following up with DPW repair crews.
One afternoon last week, Dan Dillon, the environmental group's stream monitor, visited the site of a leak discovered months ago in Herring Run Park, along Parkside Drive at Tyndale Avenue in Northeast Baltimore.
As in many parts of the city, the sewer line was laid alongside the streambed decades ago.