"natural reproduction"
Not so much for the Salmon but the Rainbow and Brown Trouts would have a better chance... yet to make it baby making factory alot has to be done to the waterway and the head waters to keep them fed. More plants above and below the surface and proper repairs to the marsh lands. Something to stop the water from overheating,controled run off from storm sewers, the reduction of salt used near the water ways and a reduction in chemical useage near waterways.
Distroying things is cheeper than fixing them...
Ken