PORTLAND – A coalition of Maine environmental groups is set to tell the state’s Board of Environmental Protection why they oppose a change in the way Flagstaff Lake’s water quality is certified.

Maine Rivers, the Natural Resources Council of Maine, the Appalachian Mountain Club and Trout Unlimited have filed an appeal of the decision with the board, which will hear the case Thursday.

Maine’s Department of Environmental Protection had withheld water quality certification from the lake for 10 years because it did not meet standards for natural lakes, where drawdowns are limited to 11 feet at most.

The department changed its stance this November and certified the lake’s quality under standards for artificial reservoirs, where water levels are allowed to drop by as much as 24 feet.

That change allows Florida Power and Light to avoid a lengthy review process that would set a separate water quality standard for the lake, but environmental groups say it could weaken standards for other Maine lakes.

Water levels at the lake, which was created by a dam in 1950, can drop by as much as 30 feet in the winter as Florida Power and Light uses water to make electricity.

Andrew Fisk, director of the Bureau of Land and Water Quality, said DEP staff have been considering both interpretations for a long time.

“We didn’t cook something up in the last six months,” Fisk said. “We’ve been thinking about both of these versions, or theories, for 10 years.

Allen Wiley, director of business and regulatory affairs in Maine for FPL Energy, said it has been his company’s position all along that Flagstaff should not be held to the standards of a natural lake.

“We think we meet the law,” he said.

The U.S. Environmental Protection Agency also opposes the new interpretation.

Stephen Silva, director of the EPA’s Maine program, said the state is overstepping its bounds by trying to make Flagstaff Lake, which is subject to unusually large fluctuations in water levels every year, conform to existing water quality laws.

He said Flagstaff should go through a separate review process that would establish a special standard for the lake.

“If you can rationalize your water quality standards this much, to fit something this unusual into them, then people might abuse that in the future,” Silva said.

Evaluating Flagstaff Lake as a natural lake would limit drawdowns to between 5 and 11 feet. That would “essentially eliminate the hydropower value of Flagstaff Lake,” said Dana Murch, dams and hydro supervisor at the DEP.

“You greatly increase flooding downstream,” he said. “You may well eliminate white-water rafting on the Dead River. You will reduce the amount of wastewater that the river can accommodate. All of those things have enormous socioeconomic impacts.”

White-water rafting companies, the Maine State Chamber of Commerce, and several towns have filed letters of support for the water quality certification with the BEP.

But others say the certification will hurt businesses.

The town of Eustis is appealing the new interpretation.

Former Eustis selectman Thomas Lemont, a retired forest ranger, said summer drawdowns lead to dry docks, canceled swimming classes and injuries suffered when people dive into water that is much more shallow than it appeared to be.