HELENA, Mont. — A judge on Friday upheld the U.S. government’s decision not to designate a Montana fish as a threatened or endangered species, after environmentalists sought to force protections for the Arctic grayling.

U.S. District Judge Sam Haddon said in his order that the U.S. Fish and Wildlife Service’s 2014 decision was based on the best available science and the agency considered all the factors required under the Endangered Species Act.

“In the absence of evidence that the agency ignored the best available scientific data, the Court must defer to the Service’s special expertise,” Haddon wrote.

The environmentalists, led by the Center for Biological Diversity, say the cold-water fish is threatened by warm water temperatures and low stream flows, which climate change will only make worse without federal protections in place.

“We are, of course, very disappointed in the court’s ruling and continue to believe, based on the science, that Arctic grayling are imperiled and should be protected,” plaintiffs’ attorney Jenny Harbine said. “We will evaluate the ruling and consider all options, including appeal.”

Arctic grayling are found in Alaska, Canada and Montana. In Montana, the fish used to inhabit up to 1,250 miles of streams in the upper Missouri River basin, but today occupies just 10 percent of that historical range.

The Fish and Wildlife Service determined in 2010 that Arctic grayling in Montana warranted federal protection, but other species took precedence. Four years later, they reversed the determination and said the fish did not warrant listing as threatened or endangered.

Scientific testing after the 2010 decision found 15 additional Arctic grayling populations with native genes, and most of those populations are on federal lands that are already strictly regulated, U.S. Department of Justice attorneys said. Nineteen of 20 populations of the fish in Montana are now stable or improving, the Fish and Wildlife Service said in the 2014 decision.

In addition, a voluntary landowner program along the Big Hole River has improved habitat for the fish, attorneys for the federal government and state wildlife officials said.

“We’re pleased with Judge Haddon’s decision because it recognizes the hard work of a diverse partnership between Montana FWP, federal agencies, conservation organizations and private landowners who have all worked very hard to restore grayling and keep them off the Endangered Species List,” Montana Fish, Wildlife and Parks director Jeff Hagener said in a statement.

Harbine praised the landowner program, but said stream flow levels are still too low, the water is too warm and the program won’t be enough to offset the effects of climate change.