BILLINGS, Mont. (AP) — A judge ruled Friday that the U.S. government can continue to use chemical retarders to fight forest fires, despite the fact that it is a practice pollutes streams in western states in violation of federal law.

Stopping the use of the red mud material could have resulted in more environmental damage from wildfires, said U.S. District Judge Dana Christensen in Missoula, Montana.

The judge agreed with U.S. Forest Service officials who said dropping retardants from airplanes into waterways is sometimes necessary to protect life and property.

The decision came later environmentalists sued following revelations that the Forest Service had dumped the retardant into waterways hundreds of times over the past decade.

Government officials say chemical fire retardants could be critical to slowing the dangerous fire. Wildfires across North America have become larger and more destructive over the past two decades as climate change warms the planet.

Over the past decade, more than 200 shipments of retardants have entered waterways. Federal officials say such situations typically occur by mistake and in less than 1% of the thousands of shipments each year.

A coalition that includes Paradise, Calif., where a 2018 wildfire killed 85 people and destroyed a town, said a court order to end the retardant’s use would put lives, homes and forests at risk.

“This case was very personal for us,” said Paradise Mayor Greg Bolin. “Our brave firefighters need every tool in their toolbox to protect lives and property from wildfires, and today’s decision ensures we have a fighting chance this fire season.”

State and local agencies rely heavily on the US Forest Service to help fight fires, many of which start on or affect federal lands.

A fire retardant is a special mixture of water and chemicals, including inorganic fertilizers or salts. It is designed to change the way a fire burns, making the flame less intense and slowing its growth.

This can give firefighters time to move flames away from populated areas and, in extreme situations, to evacuate people from danger.

“The retarder lasts and even works when it’s dry,” said Scott Upton, former regional chief and air assault team leader for the California State Fire Agency. “Water is only good because it dries up. It puts out fires very well, but it won’t last.”

The Oregon group Forest Service Employees for Environmental Ethics argued in its a lawsuit filed last year that the Forest Service is flouting the Clean Water Act by continuing to use the retardant without taking adequate precautions to protect streams and rivers.

Christensen said that ending the use of fire retardants “will likely lead to more damage from wildfires — including to lives and property, as well as to the environment.” The judge said his ruling was limited to the 10 western states where members of the plaintiff group claimed harm from pollution in the waterways they use.

After the lawsuit was filed, the Forest Service applied to the Environmental Protection Agency for a permit that would allow it to continue using the retarders without breaking the law. This process can take years.

Christensen ordered federal officials to report on their progress every six months.

Experts say climate change, people moving into fire-prone areas and overgrown forests are creating more catastrophic megafires that are harder to fight.

More than 100 million gallons (378 million liters) of flame retardants have been used over the past decade, according to the Department of Agriculture.

According to the 2021 risk assessment, the health risk to firefighters and other people who come into contact with fire retardants is considered to be low.

But the chemicals can be harmful to some fish, frogs, crustaceans and other aquatic species. A government study found dozens of threatened species could be adversely affected by improper application of the retardant, including crayfish, spotted owls and fish such as shiners and smacks.

Forest Service officials said they are trying to come into compliance with the law by getting a pollution permit, but that could take years.

To prevent stream pollution, officials in recent years have avoided falls in buffer zones within 300 feet (92 meters) of waterways. The retardant can only be used inside those areas where there is a threat to human life or public safety. Of the 213 cases of fire retardant landings in water between 2012 and 2019, 190 were accidents and the rest were necessary to save lives or property, officials said.

As the 2023 fire season begins, California Forestry Association President Matt Diaz said the prospect of a federal agency that plays a key role in fighting many wildfires without fire retardant is “horrendous.”

Much of the western U.S. received heavy snowfall last winter, and as a result, much of the region’s fire danger is lower than in recent years.