But the most devastating blow for the sockeye came from a dam-building frenzy that began in the 1930s, submerging rapids and waterfalls and creating a series of artificial lakes that stewed in the sun.
Warmer water bred disease. Slower currents meant that the juveniles often took so long to reach the ocean that they were devoured by birds and seals.
In 1979, the fish counters at the Lower Granite Dam recorded just 25 Snake River sockeye. In 1990, the count fell to zero.
The Snake River sockeye was added to the endangered species list in 1991 after a petition from the Shoshone-Bannock tribes in the spawning areas.
Hatcheries — which produce fertilized eggs that are placed in spawning areas — helped stave off extinction. In 2014, the count at Lower Granite rebounded to 2,786, the most in at least four decades.
But many scientists doubt that the current approach can prevent extinction of the Snake River sockeye as temperatures continue to rise.
"When you start reducing adult returns to the spawning grounds to the low numbers we're watching right now, it's like inbreeding — you don't get enough genetic diversity to sustain the populations," said Steve Pettit, a retired Idaho Fish and Game biologist. "That can threaten their long-term survival just as much as pure numbers can."
Still, he said it's worth trying: "The sockeye still coming back to Idaho are in my opinion museum pieces."
As of Saturday, the count at the Lower Granite dam this year was 411.
Into the truck