BILLINGS, Mont. (AP) — An environmental group filed a lawsuit against U.S. Forest Service officials on Tuesday for allegedly polluting waterways during their battles against wildfires by inadvertently dropping large volumes of chemical flame retardant into streams.

Government data released earlier this year found aircraft operated or contracted by the Forest Service dropped more than 760,000 gallons of fire retardant directly onto streams and other waterways between 2012 and 2019.

The main ingredients in fire retardant are inorganic fertilizers and salts that can be toxic to some fish, frogs, crustaceans and other aquatic species.

Tuesday’s lawsuit alleges the continued use of retardant from aircraft violates the Clean Water Act.

Government found retardant may impact species

It requests a judge to declare the pollution illegal and was filed Tuesday in U.S. District Court in Montana by Forest Service Employees for Environmental Ethics.

“It’s simply too toxic at the levels used fighting fires,” said Andy Stahl, the Eugene Oregon-based group’s executive director.

Forest Service officials in recent years have sought to avoid pollution from retardant by imposing buffer zones around waterways where drops are restricted.

A government study this year determined that misapplied retardant likely would adversely affect dozens of imperiled species, including crawfish, spotted owls and fish such as shiners and suckers.

The Forest Service received the lawsuit, but spokesperson Wade Muehlhof said it was agency practice not to comment on pending litigation.