PORTLAND, Maine (AP) Environmental groups and a Native American tribe accused the operator of a Maine dam on Monday of not fulfilling its obligation to protect the country’s last remaining Atlantic salmon river run.

The last wild Atlantic salmon live in a group of rivers in Maine and have been listed under the Endangered Species Act since 2000. The Penobscot River, a 109-mile (175-kilometer) river in the eastern part of the state is one of the most important habitats for the fish.

The Penobscot is also the site of the Milford Dam, which is owned by renewable energy giant Brookfield Renewable. The company is required under the Endangered Species Act to maintain fish passages that allow 95% of adult salmon to pass the dam within 48 hours.

According to the Natural Resources Council of Maine, Atlantic Salmon Federation and Penobscot Indian Nation, documents obtained using the Maine Freedom of Access Act show that Brookfield isn’t living up to that obligation and that data compiled by the Maine Department of Marine Resources last fall show that only about 21% of salmon pass the dam in the required timeframe.

The groups contend that the problems at the dam are longstanding and that the data illustrate that Brookfield isn’t doing enough to fix them.

“We need to see some action here because this problem has been festering for too long,” said Nick Bennett, a staff scientist with the Natural Resources Council of Maine.

A Brookfield representative declined to comment on the group’s statements.

Brookfield’s stewardship of Maine salmon has long been a point of contention with environmental groups. The company has touted its efforts to improve passage on the Penobscot and Kennebec rivers.

Salmon were once plentiful in U.S. rivers, but populations were hurt by overfishing, and factors such as dams and pollution have made restoring them difficult. The species is widely used as seafood because it is widely grown in aquaculture farms.

Salmon counters found more than 1,300 of the wild fish on the Penobscot River last year. Numbers ebb and flow from year to year, with a recent low of 503 in 2016 but more than 1,400 in 2020.

The environmental groups shared the documents they obtained with The Associated Press. The documents include an email from Dan Kircheis, a salmon recovery coordinator with the National Oceanic and Atmospheric Administration, in which Kircheis states that Brookfield is “not meeting the delay standard for Atlantic salmon.”

Kircheis declined to comment. Officials with the Maine Department of Marine Resources also declined to comment.