I have long thought that many of the exceptional large sea-run cutthroat I have seen in PS rivers were rainbow (steelhead)/cutthroat hybrids.

That said the very large cutthroat that dwell in lakes and larger beaver ponds look to be pure cutthroat.

On several occasions following very large floods I have seen exceptionally large cutthroat caught during winter steelhead seasons. I every case there has been an upstream reservoir in the system and I suspect that those fish were flushed from those reservoir. The fish consistently looked more like lake fish (heavy body) than the sleeker sea-runs.

Curt