AUGUSTA, Maine (AP) A group of environmental organizations filed court papers Thursday to try to halt operations at Maine dams to protect salmon.

Atlantic salmon are listed as endangered by the federal government. They used to swim upstream and spawn in almost every river north of the Hudson River, but now only return to Maine. The conservation groups want a judge to stop or curtail the operations at four dams on the lower Kennebec River to help the fish.

Brookfield Renewable owns the dams. The company is a subsidiary of a larger Canadian company that owns many of the dams in the state.

The groups said in a statement that the dams “create an impenetrable barrier that blocks endangered Atlantic salmon from traveling from the Gulf of Maine to prime spawning habitat on the Sandy River.”

The court action is part of an ongoing legal struggle over the fate of the dams. Brookfield sued Maine state agencies last month with a complaint that the agencies acted improperly in drafting fish passage policies.

The environmental groups’ court filing “can only serve to delay existing regulatory processes and implementation of fish passage solutions,” said Brookfield spokesperson Miranda Kessel.

The groups want the judge to shut down or limit operations at three of the four dams to make it easier for salmon to safely pass during two time periods. One is Oct. 15 to Dec. 31, when adult salmon are migrating downstream after spawning. The other is April 1 through June 30, when young salmon are migrating downstream. At a fourth dam, the organization wants the company to open up all options for salmon to safely pass.

Most of the salmon offered for sale in major grocery stores is farm raised, but wild salmon of all species are imperiled on the U.S. coasts. In Alaska, Native tribes that have relied on the fish for centuries say king and chum populations have dwindled to almost nothing.

The loss of salmon has not only hurt subsistence fishers, but also business operations such as processing facilities.