Animal manure, one of the Chesapeake Bay's oldest pollutants, also remains one of its most troublesome, contributing to "dead zones" where fish and crabs cannot live, according to a report issued yesterday.

The Chesapeake Bay Foundation, which conducted the study, said that farm manure runoff pours as much nitrogen and phosphorus into the bay as do urban sewage plants.

The environmental group said it was frustrated with efforts to halt manure pollution, saying that tons of waste from hog, dairy and chicken farms were still finding their way into tributaries of the bay.

"We are getting impatient, and I think the bay is getting impatient," foundation President William C. Baker said at a news conference at the group's headquarters in Annapolis.

The report says that manure is the source of about 18 percent of the nitrogen that ends up in the Chesapeake and about 25 percent of the phosphorus.

Those two pollutants, though not toxic, have come under scrutiny in recent years because they feed large algae blooms that suck the oxygen from bay water.

These algae were blamed last year for a dead zone of low-oxygen water that took up 40 percent of the bay.

The report says that manure, though eminently natural in origin, had become unnaturally abundant in the Chesapeake region because of huge farming operations.

The watershed's farms have 185 million animals, which produced about 44 million tons of manure last year.

In many cases, the report says, large farms produce far more manure than is needed to fertilize the nearby cropland.

But sometimes the excess manure is spread on the land anyway -- simply because there is nothing else to do with it, the report says.

Once the manure is spread on the land, pollutants can be released into the air, spread into groundwater or washed into streams, the report says.

The report suggests various possible solutions, though Baker admitted that none of them could make a difference overnight. Animal feed might be changed so that manure contains less pollutants, he said, and states might consider adding a small tax on beef or chicken to pay for cleaning up agricultural pollution.

He said that states in the bay watershed were behind on coming up with "tributary strategies" to clean up streams and rivers.

"We're trying to restart the engine" with this report, Baker said.

The report singles out areas of particularly high pollution, including Pennsylvania's Lancaster County, where dairy cows are raised, and the Delmarva Peninsula, which has massive chicken farms.

Yesterday, officials from those areas said they were putting serious efforts into change.

Jim Perdue, chief executive of Maryland's Perdue Farms, said in a telephone interview yesterday that his company had put an additive in its chicken feed that reduced the phosphorus in the manure.

In addition, he said, Perdue Farms spent $13 million on a plant to turn manure into pellets that could be shipped elsewhere in the country. But the company was having trouble finding buyers for the fertilizer pellets, he said.

"We haven't been sitting around not doing anything," Perdue said.

Attending the news conference was former Maryland state senator C. Bernard "Bernie" Fowler, who since 1970 has advocated cleaning up the bay.

Fowler, 80, said he was worried that so little progress had been made since then -- even though it was clear what pollutants were causing damage. "When that Chesapeake Bay goes," Fowler said, "the heart of Maryland stops beating."