JOHN DAY, Ore. _ Officials say more than 180 wild Chinook salmon died in a remote section of the Middle Fork of the John Day river.
The Blue Mountain Eagle reports that the die-off is due to low water and a sudden spike in water temperatures.
Staff members surveyed a 22 mile stretch of the river and found 113 Chinook still alive.
The region has been hit with an early heat wave, featuring highs of more than 100 degrees.
Jeff Neal, an Oregon Department of Fish and Wildlife fish biologist in John Day, says water temperatures in the river rose from 62 degrees on June 26 to a high of 74 degrees the next day.
Biologists say wild adult Chinook salmon can survive in temperatures of 80 degrees, but only as long as the rise in heat is gradual.
Some other fish, including small whitefish and sculpin, also died in the warming water.
To prevent future die-offs, environmental officials are looking at narrowing the channel and planting more trees to shade the river.