We should work to preserve healthy runs and restore depressed runs as many ways as possible without screwing with the gene pool. The second you start playing God, to say, is the second those fish are no longer native.

Just because a river is an ESU or rivers are side by side does not mean the fish are genetically similar enough to cross breed to propgrate a river's native steelhead population without changing the genetic makeup of that steelhead population.

Hell, fish that spawn in certain sections of rivers can be distinct in behavior, appearance etc.