Rookie,

Hatchery steelhead should bear an adipose fin clip on all western Washington rivers except:

Quinault, Cook Creek, Queets, Salmon, which are from Quinault Tribe and U.S. Fish & Wildlife rearing facilities. There might be others, but I'm not familiar with them. I think the Hoh Tribe marks their hatchery steelhead.

The Cowlitz River has some late winter run steelhead bearing a ventral fin clip, but I think you are required to release them anyway, unless caught above the Cowlitz dams, in which case you can retain them. I've gotten this wrong before, so check before bonking any.

Steelhead broodstock programs sometimes use the ventral fin clip as a mark. Whether you can retain those fish may vary by river system, so check your regs.

Sincerely,

Salmo g.