Underwater video from a Columbia River tributary in south central Washington shows sockeye salmon infected with fungus caused by heat stress. They’re hiding out in the cooler waters of the Little White Salmon River, far from their spawning grounds.

After the heatwave, water temperatures in many parts of the Columbia River rose beyond the 68-degree high that salmon can stand. Above that, the fish can potentially die.

In 2015, the heat and low river flows caused nearly 99% of the sockeye salmon to die before they reached spawning grounds. The heat wave timing was fortunate for sockeye runs, said Ritchie Graves, Columbia Hydropower Branch chief with NOAA Fisheries.