PORTLAND (AP) – Sappi Fine Paper North America has pulled out of a historic deal to remove a dam on the Presumpscot River to allow sea-run fish to swim upstream.

When the agreement between Sappi and conservation groups was announced a year ago, it was hailed as a turning point in the long-running battle over fish access on the Presumpscot River, which runs from Sebago Lake to Casco Bay.

But Sappi, which owns the former S.D. Warren paper mill in Westbrook, pulled out in the last several weeks without public notice or explanation.

State officials said they think the cost estimates for the work came back higher than anticipated, prompting Sappi to rethink the deal.

“I think they just made a determination that the cost was going to be too great for them. We’re all kind of regrouping here a little bit,” said Pat Keliher, director of the Bureau of Sea Run Fisheries and Habitat in the Maine Department of Marine Resources.

Under last summer’s preliminary agreement between Sappi and Friends of the Presumpscot River and other conservation groups, the Cumberland Mills dam in Westbrook would be removed by 2011. Sappi also agreed to install fish passageways, such as ladders or lifts, at upriver dams over time.

At the time, the mill’s manager said the project would cost the company in excess of $10 million: about $6 million to remove the Cumberland Mills Dam and restore the riverbed and another $4 million for upstream fish passage.

The removal of the dam, which has blocked the Presumpscot since the late 18th century, would open another section of one of the country’s first industrial waterways to migratory fish. The dam is the first obstacle for blueback herring, alewives and other fish that swim upriver from Casco Bay.

The Friends of the Presumpscot River and the Department of Marine Resources have now filed a request with the commissioner of the Inland Fisheries and Wildlife Department to require a fish passageway at Cumberland Mills. A state law allows the department to take such action in the interest of fisheries.

Meanwhile, the leader of the Friends of Sebago Lake, a group that opposed the agreement with Sappi, said the deal’s collapse is good news for the river and its fish.

Roger Wheeler said the deal included too many compromises with Sappi, but that forcing the company to install a fish passage at Cumberland Mills would compel the company to create fish ladders upstream at a faster pace than the agreement would have.

The agreement also wouldn’t have allowed salmon and other fish to swim all the way up the river

“We want to restore the fish all the way up to Sebago Lake. That’s the way it should be,” he said.