Thanks for the really interesting question! Steelhead trout live in streams and creeks from Santa Maria in the Central Coast of California all the way to the border with Mexico. As you know, these fish have been declared to be endangered because of peoples’ alteration of their habitat, water quality issues, and the introduction of non-native invasive species.

After a bit of research, I could not find any mention of steelhead trout being found in the creeks or wetlands of the Channel Islands. While, as you mention, there are sources of fresh water on Santa Cruz Island, they may be too spread out and too small to support the spawning of steelhead.

Steelhead are anadromous, meaning that they are born in fresh water, live in the ocean, and then return to fresh water to spawn. I speculate that the relative lack of access to fresh water streams on the Channel Islands from the ocean prevents steelhead from spawning on there.

Life, however, can persist and show up in the most difficult of conditions. So it is possible these fish are present, but we have not observed it. More research may be required!