(Reuters) - U.S. fishing and conservation groups sued the Environmental Protection Agency on Thursday, seeking to protect wild salmon threatened by rising water temperatures attributed in part to climate change in two major rivers of the Pacific Northwest.
The lawsuit, filed in U.S. District Court in Seattle, is believed to be the first court case brought against the EPA under President Donald Trump's newly confirmed chief of the agency, Scott Pruitt.
The groups' legal bid on behalf of salmon runs in the Columbia and Snake rivers hinges on the EPA's authority under the Clean Water Act to regulate excessive temperatures in those rivers as pollutants.
The lawsuit seeks to compel the EPA to thus require dam operators in the Columbia and Snake watersheds of Washington state, Oregon and Idaho to control river flows in such a way as to keep water temperatures cool enough for the salmon to survive.
The plaintiffs, including Idaho Rivers United and the Pacific Coast Federation of Fishermen's Associations, have argued those dams create stretches of artificially slow or shallow waters susceptible to increasingly warm weather, a regional consequence of climate change.
The lawsuit cites the EPA's own recognition in 2015, amid a major salmon die-off in the Northwest that year, of the "critical" need to lower river temperatures in the face of human-caused global warming.
It also noted that Pruitt, a former Oklahoma attorney general who sued the EPA more than a dozen times on behalf of his oil-producing state, is on the record as doubting the science of climate change.
The EPA declined to comment on the suit.
Excessively warm stream temperatures were to blame for the loss of an estimated 250,000 adult sockeye salmon in 2015 during the fishes' seasonal upstream migration from the Pacific to freshwater spawning grounds.
Summer water temperatures in the rivers has for years exceeded limits allowed under state standards, a pattern that should have prompted the EPA to craft a plan setting temperature limits and steps to take should those levels be exceeded, according to the lawsuit.
It said the EPA in 2000 began such a process tied to imperiled salmon and steelhead trout and issued a draft plan citing dams on the Columbia and Snake rivers as primary contributors to excessive water temperatures.
The suit seeks a court finding that the EPA has violated the Clean Water Act by failing to set maximum temperature levels in the impaired streams and unlawfully delayed a regulatory remedy, resulting in "severe" consequences for endangered and threatened fish populations.
Reporting by Laura Zuckerman in Salmon, Idaho; Editing by Steve Gorman and Sandra Maler