Idaho Department of Fish and Game officials say supply valves that control water delivery to two of the hatchery's 11 incubator stacks were blocked reducing inflow to a trickle. The problem was discovered Thursday and affected two Chinook salmon release groups.
The South Fork Summer Chinook group was reduced by about 35,000 fry, or about 3.3 percent of inventory. The Johnson Creek Summer group was reduced by 25,400 fry, or 8 percent.
The fish are released in an effort to supplement natural fish production in those Salmon River tributaries.
Officials say the problem is the first in 30 years at the McCall hatchery.