BOISE -- Almost 200,000 Chinook salmon are dead after freezing temperatures plugged a pipe at the Clearwater Fish Hatchery facility on the Lochsa River.

Water flows to an acclimation pond were shut off Friday. The salmon smolts that were killed were scheduled to be released into the river that day. Smolts are young salmon ready to begin their migration to the ocean.

The Idaho Fish and Game Department blames unusual cold and human error for the accident.

Hatchery attendants, who are supposed to clear ice from the intake pipe regularly, failed to notice the plugged valve.

Clearwater basin hatcheries are part of a federal program to replenish fish losses from four dams on the lower Snake River.