A federal judge on Monday will hear arguments in a Montana lawsuit that seeks to curb the U.S. Forest Service’s use of aerial fire retardant to combat wildfires over concerns that it is polluting streams and rivers.

The Forest Service Employees for Environmental Ethics, the Oregon-based group that filed the lawsuit, argues that dropping retardant in waterways without a permit violates the Clean Water Act and does more environmental harm than good in fighting fires.

But the Forest Service says it’s a critical firefighting tool. And a coalition of opponents, including a California city destroyed by wildfire, argue that limits on the use of the retardant could put more homes and forests at risk.

The case is being watched because it could impact how U.S. wildfires are fought. And it comes as the 2023 fire season gets underway following years of larger and more devastating wildfires.

Why is aerial wildfire retardant being challenged?  

The lawsuit, filed in U.S. District Court in Montana, asks that a judge issue an injunction blocking officials from using aerial retardant in waterways until they get a permit to discharge pollution as required by the Clean Water Act.

One Department of Agriculture report found retardant was likely to adversely affect 32 aquatic species. More than 100 million gallons of it were used during the past decade, according to the department.

Health risks to firefighters or other people who come into contact with fire retardant are considered low, according to a 2021 risk assessment commissioned by the Forest Service.