Sorry for the confusion
Directly from the Id F&G
What Is A Steelhead?
Steelhead are rainbow trout longer than 20 inches in length in the Snake River drainage below Hells Canyon
Dam, the Salmon River drainage (excluding lakes and the Pahsimeroi and Lemhi rivers), and the Clearwater River
drainage (excluding that portion above Dworshak Dam
and lakes). Rainbow trout longer than 20 inches in length
with the adipose fin clipped (as evidenced by a healed scar) are defined as steelhead in the Snake River from

Hells Canyon Dam upstream to Oxbow Dam, and in the Boise River from its mouth upstream to Barber Dam, and
in the Payette River from its mouth upstream to Black Canyon Dam, during steelhead seasons.