Westbrook’s Sappi paper mill will remove the Cumberland Mills Dam to open the Presumpscot River to migratory fish.

The plan is part of a preliminary agreement announced Tuesday between the paper company and Friends of the Presumpscot River, American Rivers, the Maine Department of Marine Resources and the U.S. Fish and Wildlife Service. If finalized, the dam would be removed and the waterway operational by May 2011.

Sappi would also institute a “trap and truck” program that would catch fish at the Saccarappa Dam and transport them upriver to jump-start the restoration of native fish impeded by the dam. Coupled with the removal of the Cumberland Mills Dam, it is estimated to cost Sappi $6 million.

The Saccarappa Dam itself is expected to see fishways installed by 2016 to allow fish to migrate on their own.

“It’s been a very long fight,” said Dusti Faucher, president of Friends of the Presumpscot River, a conservation group working on restoring water quality and natural habitats of the river. “We’re very pleased where we are.”

“It’s a big step for us,” said John Martis, managing director of the Westbrook Sappi mill. “We’ve been strong supporters of the environment for a while.”

“I’m truly pleased to hear that a preliminary agreement has been reached,” said Dan Martin, commissioner of the Maine Department of Inland Fisheries and Wildlife.

Earlier this year a petition was presented to the department to begin proceedings to determine whether Sappi should be required to either remove the Cumberland Mills Dam or to install fishways. Sappi originally requested hearings, at which it was expected the company would argue against any new requirements, citing cost concerns.

Martin said the tentative agreement announced Tuesday circumvents the need for the hearings, and he intends to honor a request to hold off on the proceedings when Sappi formally requests a stay.

“It’s a real tribute to the staying power of citizens,” Faucher said.

Because the deal Sappi reached is preliminary, Martin expects the stay to hold through Dec. 1, when the deal should be finalized. If the deal is not finalized, the hearings would then commence to work through the details of what needs to be done at the dam.

The Presumpscot River and its dams have long been a point of contention for conservation groups. In 2002 the Smelt Hill Dam in Falmouth was the first dam to be removed after it was damaged, leaving nine dams along the river between the ocean and Sebago Lake. Of those, all but two are hydroelectric dams, and eight are owned by Sappi. The dams prevent sea-run species of fish like Atlantic salmon from traveling from the ocean to fresh bodies of water to spawn. In addition to salmon, other sea-run fish native to the Presumpscot river are blueback herring, alewife and shad.

Many of the dams previously had fishways installed in them, though after years of neglect and aging they were no longer operational, according to Faucher.

Once the Cumberland Mills Dam is removed and fish begin migrating up to the Saccarappa Dam in sufficient numbers, Sappi will then install the fishway, which is expected to happen by 2016. Fish migration farther upstream in sufficient numbers again will require Sappi to install fishways at higher dams, such as the Mallison Falls Dam and Little Falls Dam.

John Martis, managing director of Sappi’s Westbrook paper mill, announces on Tuesday at Riverbank Park that Sappi has reached a preliminary agreement with government and conservation groups to remove the Cumberland Mills Dam. Seated are Ann Mills, left, executive vice president of the national conservation group American Rivers, and Dusti Faucher, president of Friends of the Presumpscot River.