The Hoopa and Yurok tribes and Humboldt County sought the releases to stave off an outbreak of a gill-rotting disease — known as Ich, short for Ichthyophthirius multifiliis — that spreads in low and warm water conditions.

Ichthyophthirius multifiliis, or "ich," was last measured in large quantities in the Klamath during a 2002 drought, when it may have killed many as 70,000 Chinook salmon and steelhead trout, said Michael Belchick, a biologist for the Yurok Tribe.