The plan is being published in Wednesday’s Federal Register.
It calls for applying the endangered species designation to Atlantic Salmon from the Androscoggin, Kennebec, and Penobscot Rivers.
The fish are already listed at the Dennys, along with Cove Brook and the East Machias, Machias, Pleasant, Narraguagus, Ducktrap, and Sheepscot Rivers.
The expanded area would cover the Androscoggin eastward to the Dennys River in Washington County.
The National Marine Fisheries Service and the U.S. Fish and Wildlife Service originally floated the proposal in 2006, but it was shelved pending further study.