The Department of Inland Fisheries and Wildlife has ruled that the Sappi mill in Westbrook must construct and maintain a fish passage at the Cumberland Mills Dam on the Presumpscot River.

The Conservation Law Foundation called the ruling a “major step” toward bringing migrating fish back to the river and the first decision in more than a century under a state statute that requires dam owners to maintain fish passages.

Local environmental groups say they’ve worked for more than a decade to try to get fish passage on the river, which they hope will restore the area’s health to what it was more than a century ago.

“It’s been a long, hard fight, and we are so grateful for this decision,” said Dusti Faucher, president of Friends of the Presumpscot River.

Douglas Watts, executive officer of Friends of Sebago Lake, said the ruling isn’t only good news for the health of the river, but for the eventual restoration of Sebago Lake, as well.

“We’re ecstatic about this,” said Watts.

The ruling was the result of a proceeding initiated by Friends of the Presumpscot and American Rivers in 2006 after the U.S. Supreme Court upheld conditions in federal licenses that require the mill to maintain fish passages at its other dams. The Cumberland Mills dam is not regulated by a federal license, however, because it does not produce power. Therefore, the Supreme Court decision did not apply to that dam.

“It’s the key that unlocks the rest of the river,” Faucher said about the Cumberland Mills Dam.

Faucher said it would take time to rebuild the river’s habitat, but she sees a complete restoration of the species of fish and animals that used to live in and along the river. And eventually, she said, it will be the people of Maine, through recreation and tourism, who will benefit from that restoration.

“Prior to the Industrial Revolution, the Presumpscot was teeming with Atlantic salmon, shad and river herring,” said Sean Mahoney, director of the Conservation Law Foundation’s Maine Advocacy Center. “But for more than a century, we literally turned our backs to the Presumpscot River, dumping all manner of industrial waste into it and in the process making it known more for its stench and ability to peel paint than for anything else. Since passage of the Clean Water Act almost 40 years ago, we have made great strides in restoring the water quality of the Presumpscot and other rivers around the state. This decision brings us one step further in that process.”

According to Deborah Turcotte, spokeswoman for the Department of Inland Fisheries & Wildlife, the next step will be for the department to figure out what type of fish passage Sappi will be required to install. She said a timeline for that process has not yet been set.