Two conservation organizations and a river activist have sued federal agencies demanding Endangered Species Act protection for Atlantic salmon in the Kennebec River.

The Center for Biological Diversity, Friends of Merrymeeting Bay, and Douglas Watts filed the suit Monday in Portland against the U.S. Fish and Wildlife Service and the National Oceanic and Atmospheric Administration Fisheries Division.

The plaintiffs say the once legendary salmon runs on the Kennebec are on the verge of disappearing and the federal agencies have failed to step in. The federal government declared salmon in several Maine rivers to be formally protected under the act in 2000, but did not include salmon in the Kennebec and other large rivers in central and southern Maine.