Both steelhead and rainbow trout are Oncorhynchus mykiss. They are a unique species in that individual fish develop differently depending on their environment. While all O. mykiss hatch in gravel-bottomed, fast-flowing, well-oxygenated rivers and streams some stay in fresh water all their lives and are called rainbow trout. The ones called steelhead migrate to the ocean where they spend 2 or more years before returning to their natal stream to reproduce, they then can return to the ocean to start the cycle over again. While at sea they develop a slimmer profile, become more silvery in color, and typically grow much larger that rainbow trout.
Each river has its own genetic strain of fish and each strain must be preserved if steelhead as we know them are to survive. Unfortunately, the Carmel River strain of steelhead needs help. Their numbers once in the twenty thousands are now in the hundreds. Much effort has been made by CRSA and others to rescue and rear steelhead from the drying river and its tributaries.