Watermen in Maryland, frustrated by declining seafood harvests and "dead zones" in the Chesapeake Bay, are preparing a class-action lawsuit against polluters that could include municipal sewage plants and farming conglomerates.

Larry Simns, the president of the Maryland Watermen's Association, said yesterday that the group considered its first-ever lawsuit against polluters as a new tactic to force improvements in the bay's water quality.

"We've been trying to get everybody to do stuff about it," he said. "And we just don't see any results."

Simns notified watermen of the potential suit in a memo sent out July 14. He said the association's executive council had voted unanimously in April to work with Washington attorney John Coale on the first stages of the lawsuit. Yesterday, Simns stressed that the plans were in the early stages: "We haven't decided what we're going to do."

But he and Coale said that they are researching who might be sued by the watermen. Among those suggested are large and small cities operating sewage plants, and large-scale farming operations. These have been cited by scientists as major sources of the pollutants nitrogen and phosphorus, which feed the algae blooms that cause "dead zones" in the bay.

Simns said that the suit would probably not target Maryland farmers but that he was interested in targeting Pennsylvania operations. That state dumps more nitrogen into the bay's watershed than any other, according to scientists.

"We're going to look at Pennsylvania hard," Simns said.

Coale, a veteran of class-action suits against tobacco companies, said the Chesapeake's pollution could be compared to the damage caused by the wreck of the Exxon tanker Valdez in Alaska in 1989.

"We see this as like a Valdez case," he said. "But rather than polluting in an hour, they've done it over . . . decades."

Coale said that he had been talking with Simns about the suit for a year. He said watermen might base part of their suit on a claim that polluters had violated federal clean-water laws. He said they might also claim that polluters damaged the ability of the state's 7,313 licensed watermen to work.

He said the suit probably would be filed in federal court in Baltimore, and could seek billions in damages as well as an end to pollution.

"We're going to ask for a boatload of money, but our number one priority is to do something for the bay," he said.

The plans come during a time of high frustration in the Chesapeake region, after a disastrous year last year in which a low-oxygen "dead zone" encompassed 40 percent of the bay, and scientists saw a sharp drop in the amount of underwater grasses -- a crucial part of the bay ecosystem.

Also this year, the Chesapeake Bay Foundation has vowed to file additional lawsuits against polluters and government agencies that it believes aren't doing enough.

And watermen and recreational anglers have reported a resurgence of the dead zone in the upper bay.

"This dead zone is like heart disease," said Richie Gaines, president of the Chesapeake Guides Association. "You can't see it, you can't feel it, you can't tell it's there. But it's dying on the inside."

However strong the proof of the bay's pollution, it might still be hard to win a massive class-action suit against polluters, said John C. Coffee Jr., a professor at Columbia University's school of law.

Coffee said that another class-action case concerning the Chesapeake Bay decades ago, filed over a pollutant called kepone, was helped by the fact that just one company was blamed for the pollutant. In this case, he said, it might be hard to convince a judge that sewage plants, farmers and government agencies could be lumped together in the same suit.

"You're looking at a very diverse set of defendants who have very different stories and very different contributions to the overall pollution," he said.

Staff researcher Bobbye Pratt contributed to this report.