MONTPELIER, Vt. – It may take decades for Vermont to clean up Lake Champlain, where phosphorus flowing in from farms, sewage treatment plants and suburban lawns has fed toxic algae blooms in recent summers, lawmakers were told Wednesday.

The assessment came from multiple witnesses who testified at a meeting of four legislative committees, whose members were getting an update on work under way by the state Department of Environmental Conservation and the U.S. Environmental Protection Agency to come up with new pollution limits for the lake.

The effort to revise the limits was triggered by a lawsuit filed by the environmental group Conservation Law Foundation against the EPA in 2008. The group charged a 2002 version of the limits didn’t bring the lake into compliance with water quality standards under the federal Clean Water Act. The case was settled in 2010, and the EPA began work on the revisions early last year.

Despite working to reduce phosphorus-laden runoff for more than a decade, Vermont cannot show it has made much progress, Environmental Conservation Commissioner David Mears said in an interview. Asked how long it might take, he said, “Decades is the right scale to think about it.”

One problem is a lack of sufficient money, either at the state or local level for work like helping farmers reduce runoff, helping cities and towns better manage sewage plant discharges and storm runoff and educating homeowners about using less fertilizer in their yards, officials said.

During the morning hearing, Sen. Virginia Lyons, chair of the Senate Natural Resources and Energy Committee, asked Steven Perkins, director of ecosystem protection for EPA’s regional office in Boston, about federal funding to implement the new plan to limit pollution when it is completed, most likely next year.

“The long-term picture, particularly as it relates to implementation, is tricky,” Perkins said.

Lyons said she was hoping for federal assistance. “Doing the right thing … is extremely expensive for a little state,” she said.

The 125-mile-long Lake Champlain divides northern New York and Vermont and extends into Canada. Louis Porter, lake keeper with the Conservation Law Foundation, said New York has a separate set of limits that have not been deemed out of compliance with the Clean Water Act.

Another problem facing the lake is silt from erosion in the rivers feeding it, Buzz Hoerr, chairman of a Vermont citizens’ panel that oversees the lake, later told a House committee during a separate hearing.

River flows had been speeded up through human mismanagement of the streams, he said. Straightening rivers and lining banks with large stones so that roads or railroads could be built next to them leads to much more erosion than if the streams are left to meander and dissipate energy into adjacent wetlands, he said.

He said Vermont needs to “get away from the culture of drainage” that had governed too much river management during the last 200 years and “just slow things down.”

Hoerr said afterward that he did see one encouraging development: a consultant for the state Department of Environmental Conservation has done detailed mapping of farmland in the Misissquoi River valley in northern Vermont. The river empties into the lake. The map identifies several “critical source areas,” usually farm fields that because of their slope or closeness to the Misissquoi or its tributaries, are adding heavily to the phosphorus problem.

“Eighty percent of the runoff has been isolated to 20 percent of the fields,” Hoerr said.

Mears said later that the information could help the state focus its assistance, and possibly its regulatory enforcement, on specific farms.