PORTLAND, Ore. (Reuters) - Federal officials in Oregon have been trucking hatchery salmon more than a hundred miles (160 km) north to another hatchery in Washington state throughout July to preserve fish that had been dying off by the thousands in an unseasonably warm river.

Water that would rarely top 70 degrees Fahrenheit (21 Celsius) at this time of year in the Warm Springs River has reached 76 (24.4 Celsius), hot enough to weaken juvenile spring salmon immune systems, U.S. Fish and Wildlife Service fisheries supervisor Rich Johnson told Reuters on Wednesday.

About 2,000 of the fish were dying every day before they were relocated, he said.

“If the weather continues warm, there could be more problems for fish,” Johnson said, noting that river temperatures across the region spiked a full month earlier than usual this year.

The effort to save Warm Springs National Fish Hatchery’s 160,000 remaining baby fish – plus 680 adults - comes as state wildlife officials in both Oregon and Washington have imposed rare fishing restrictions.

High temperatures have been blamed for hundreds of thousands of wild and hatchery fish deaths throughout the U.S. Pacific Northwest.

At central Oregon’s Rock Creek Hatchery, a mechanical error that halted water flow was made worse by high water temperatures in June, killing 400,000 pre-smolt spring Chinook salmon.

Washington and Oregon state wildlife officials have reported hundreds of wild fish found dead along riverbanks in both states over the past month as well.

The salmon at Warm Springs National Fish Hatchery were particularly vulnerable because of their location east of the Cascade Mountains, Johnson said.

Despite its name, there are no warm springs nearby, but low snowpack on nearby Mount Hood has left the hatchery with little of the chilling runoff that would normally cool its waters, he said.

After rejecting a proposal to chill the water at Warm Springs as too expensive, officials opted instead to transport the fish to Little White Salmon National Fish Hatchery in Washington, located on the much cooler Columbia River, Johnson said.

“We will hold these little fish at little White Salmon until around October, when the temperatures cool, then we will move them back to Warm Springs to let them finish maturing there,” he said. Once the salmon mature enough, they are tagged and released into the wild.