After 13 years, the Federal Energy Regulation Commission has issued Westbrook-based Sappi Fine Paper a new operating license for the Eel Weir Dam, establishing a new Sebago Lake-level management regime for the next four decades.

The new requirements, which could lead to lower lake levels in the late summer, have buoyed environmentalists, who have criticized past lake-level plans, but they also worry boating interests on the lake, including homeowners and marinas.

The depth of Sebago Lake, the second largest in Maine, is controlled by the 1,350-foot-long, 22-foot-high dam, located at the head of the Presumpscot River, which flows to the ocean through Gorham, Standish, Windham, Westbrook and Falmouth. Under the new plan, the lake would rise higher in periods of significant rain or melting snowpack, while in periods of drought, the lake would be lower, mimicking a more natural cycle.

Since 1997, the lake has been managed in accordance with the commission-approved Lake Level Management Plan, which set six seasonal lake-level targets ranging between 262.5 feet mean sea level (msl) and 266.65 feet msl, with the highest levels required between May and June and the lowest at the beginning of November. The new plan contains only one seasonal target – that the lake level measure 266 feet msl between May 1 and June 15 every year.

In place of the predominantly fixed-target regime, the commission approved a flow-based regime, which enables Sappi to manage levels more flexibly between the range of 262 and 266.65 feet msl. Sappi now is required to run a total minimum water outflow into the Presumpscot River when lake levels reach the low of 262 feet msl. The new flow regime is supposed to maintain an adequate supply of oxygen for fish in the Presumpscot River, which is popular among fishermen.

Sappi’s previous, 30-year dam operating license expired in 2004. The company applied for a new license in 2002. Brad Goulet, Sappi’s hydro manager, declined to comment Wednesday on the long-awaited license.

According to Ann Miles, the director of the federal commission’s Office of Energy Projects, the new regime will lead to greater variability in lake levels, a goal long sought by the environmental advocacy group, Friends of Sebago Lake, which has argued that the previous management plan has eroded the lake’s beaches, harmed its wetlands, and caused a consequent decline in water quality.

“Under average inflow conditions, S.D. Warren’s proposed operation would increase flood storage and decrease lake levels throughout most of the year when compared to current operation under the (lake level management plan),” Miles wrote. “Commission staff concluded that there would be some benefit under the flow-based regime from less shoreline erosion associated with more frequent lower lake levels, but the flow-based regime would result in lower lake levels during the recreation season, especially during dry, low inflow years.”

Under the previous plan, lake levels were required to hit 265.17 feet msl on Aug. 1. Under the new plan, the only requirement in August is that Sappi pump through a minimum outflow level if levels reach as low as 262 feet.

Members of the Sebago Lake boating community find the new flexibility – especially during the recreational boating season – concerning. Charles Frechette, the owner of Sebago Lake Marina in Sebago and an outspoken advocate of uniform water levels for decades, said he was concerned by the new license, which could force marinas in shallow parts of the lake to extend their docks.

Stephen Kasprzak, a past president of Friends of Sebago Lake, and a longtime advocate of lower lake levels, said he was “pleased” by the new water level regime.

“It certainly is better than what we have been operating with,” he said. “It will reduce the amount of beach and upland erosion that has been occurring. I think it will help restore the wetland function.”