Of course it depends on your definition of catastrophic. I think its not a very far stretch to imagine that, if the OP were to be covered with ice, it would be catastrophic to the flora and fauna of the region. No?

Remember, as Os said there have been many ice ages. Steelhead as a species have outlived at least the last of them. I'm far less concerned about the ability of the steelhead to survive such an occurrence than I am that of modern humans. Forensic anthropologists for the most part think our species of hominid barely survived the last one.

"That doesn't mean I should sacrifice the needs and desires of those that follow me to satisfy my own greed and selfishness."

Recreational anglers would do well to consider this statement in the context of declining native runs.