Data shows that fish survival past modernized dams can be as good or better than naturally flowing rivers. Technological improvements at dams, including scientifically engineered fish ladders and surface passage systems—like removable spillway weirs—help fish safely navigate the dams. Research by NOAA Fisheries shows that with the improvements that have been made, the survival of juvenile fish past the eight dams on the lower Columbia and lower Snake rivers is better now than when the Snake River was free flowing.

Proceedings of the National Academy of Sciences of the USA – Ocean and dam influences on salmon survival
Public Library of Science – Survival of Migrating Salmon Smolts in Large Rivers with and Without Dams