Pennsylvania Pollution Muddies Bay Cleanup

But many farmers, not wanting to yield a competitive advantage, are not easily convinced.

"You're barely making it as it is," said Earl Newcomer, a retired Lancaster County farmer who has worked with conservation groups. "If you change it, it might get worse."

When farmland is replaced by subdivisions and shopping malls, environmentalists have said, the problems might get worse. The acres of concrete prevent rainwater from soaking into the soil -- instead, the waster blasts through storm drains into streams, sending gluts of polluted mud downstream.

Those who have worked on the problem here in Lancaster said their job is tougher because the problem is so diffuse: It's not a single factory belching technicolor ooze.

"You can't just point to a pipe and say, 'There's the reason for all the pollution, and there's the guy who owns the pipe,' " said Mark Metzler, a scientist who has studied the Little Conestoga.

"You don't have any real major problem," in Lancaster, Metzler said, just a thousand smaller problems such as farms, houses and shopping malls. "But when you put them all together, you get a good-sized mess," he said.

As Pennsylvania's efforts to deal with pollution continue, the state faces a deadline. For decades, much of the sediment washed out of Pennsylvania has not actually flowed into the Chesapeake -- instead, it has piled up as silt behind the Susquehanna's dams: Safe Harbor and Holtwood in Pennsylvania and Conowingo in northern Maryland.

All the dams but the giant Conowingo are full, said Robert Walter, a research associate at Franklin and Marshall College in Lancaster. By 2020, he said, the Conowingo, too, is expected to hit its limit, and all of Pennsylvania's runoff will be spilling into the bay.

"When that last dam is filled," Walter said, "that's going to be a catastrophic release."