FLAGSTAFF, Ariz. (AP) – Critics of a plan to expand a ski resort on an Arizona mountain are suing the U.S. Forest Service in what has been a yearslong battle to protect a site considered sacred by American Indians.

The lawsuit filed Monday comes more than three months after the U.S. Supreme Court denied an appeal from tribes that said the use of treated wastewater to make artificial snow on the mountain threatened their religious and cultural survival.

The lawsuit filed by the Save the Peaks Coalition and a group of citizens contends the Forest Service failed to consider the human health risks of ingesting snow made with treated wastewater at the Arizona Snowbowl resort outside Flagstaff.

“By approving treated sewage effluent for snow making without adequate analysis, the government essentially turns the ski area into a test facility with our children as the laboratory rats,” said Howard Shanker, an attorney for the plaintiffs. “That is unconscionable.”

The Forest Service and former Coconino National Forest Supervisor Nora Rasure are named as defendants. Coconino forest spokeswoman Karen Malis-Clark declined to comment, citing pending litigation.

A panel of the 9th U.S. Circuit Court of Appeals previously sided with tribes who asserted that drinking water tainted by runoff from the man-made snow could pose health risks. The full court later overturned the decision, saying the plaintiffs never properly raised the issue in the lower court, according to the lawsuit.

Shanker, who represented tribes in the previous lawsuit, called it a “ridiculous assertion” that left the door open for refiling. He said this case likely would not reach the U.S. Supreme Court.

The lawsuit contends that treated sewer water has been found to contain pharmaceuticals, hepatitis, industrial pollutants and drugs that could be harmful to children playing in the snow and to skiers. The plaintiffs are asking a judge to determine that the environmental analysis is inadequate.

Snowbowl general manager J.R. Murray said officials remain focused on planned improvements at the resort despite the lawsuit and are looking forward to an expected snowy winter season.

He declined to comment directly on the lawsuit but said: “You tend to believe when the Supreme Court makes a ruling, that puts some finality to it. But I guess in America, people can sue for whatever reason. Whether it has merit, that has yet to be seen.”

Snowbowl officials have said the snowmaking equipment is necessary to ensure the survival of the ski area, which opened in 1937 and has struggled with short seasons because of a lack of snow. The Snowbowl is privately owned and operated by Arizona Snowbowl Resort Limited Partnership.

The 777-acre resort wants to spray man-made snow, add a fifth chair lift and clear about 100 acres of forest to extend the ski season on the western flank of the San Francisco Peaks that have spiritual and religious significance to 13 Southwest tribes.

The resort operates under a special use permit with the Forest Service. Work to produce artificial snow using reclaimed water piped about 15 miles from Flagstaff is set to begin next spring. Snowbowl officials are hoping for more than 100 days of skiing per season, but the lawsuit is asking for an injunction to delay improvements until the complaint runs its course.

Snowbowl owner Eric Borowsky said the lawsuit appears to be “just more of the same from the Flagstaff activists network.”

“I think this matter has already been addressed in the previous litigation, but the courts will have to make that decision,” he said.