More than 700,000 sockeye salmon are expected to swim up the Columbia River in the US state of Washington this summer, but hot weather in the US Pacific Northwest has made their journey much more difficult.

The Seattle Times reports that in the Okanogan River, a Columbia River tributary in Washington, water temperatures hit 80 degrees Fahrenheit earlier this month, causing sockeye to wait at the river's mouth instead of starting their journey up the river system to spawn. 

The area has confronted such heat before. The newspaper reports that a quarter million sockeye died in 2015 from the heat.

"I think there is a good chance that happens again, barring a break in temperatures or a rain event," Cody Desautel, the executive director of the Confederated Tribes of the Colville Indian Reservation, told the Times.

Tribes have looked at trucking fish to their spawning grounds across the US border with Canada, but that would only save a fraction of the run. Fisheries managers in the US state of Idaho have similarly considered trucking fish to their spawning grounds to avoid hot river temperatures.

The Seattle Times goes on to report that the large run is largely due to better management and an influx of federal funding to preserve and rehabilitate salmon habitat in the region. However, hotter weather has hit the area and is sticking around longer.