Steelhead are native rainbow trout which migrate to the ocean as juvenile fish and return to fresh water as adults to spawn. In Idaho these ocean-going trout are often classified into two groups, A-run and B-run based on their size and ocean life history.
Idaho’s A-run are usually found in the Snake and Salmon rivers. They return from the ocean earlier in the year (usually June through August) and they most often return after spending one year in the ocean. Because of their early return and short stay in the ocean they usually weigh 4 to 6 pounds and are generally 23 to 26 inches in length.
B-run steelhead most often return to the Clearwater River, but some return to tributaries in the Salmon River. These fish usually spend two years in the ocean and start their migration to Idaho later in the summer or fall of the year (usually late August or September.) Because of the extra year and the extra summer of growing in the ocean, they return as much bigger fish. Average B-run steelhead weigh between 10 to 13 pounds and are 31 to 34 inches long.
Steelhead grow even larger when they spend a third year in the ocean before they return to Idaho to spawn. These steelhead are usually larger than 37 inches and can weigh more than 20 pounds.
The Idaho state record steelhead was 30 pounds and 2 ounces and was caught in the Clearwater River in 1973.