The four lower Snake River dams and the reservoirs they create harm fish in numerous ways. 

1. The dams kill juvenile fish as they pass each structure on their migration to the Pacific.
2. The dams inundate 140 miles of spawning and rearing habitat, and create slow moving reservoirs that are devoid of food, become lethally hot in the summer, and lack cover fish can use to hide from predators.
3. The dams cause juvenile fish to expend much more energy to migrate to the Pacific because the fish must actively swim through reservoirs instead of migrating passively with river current.
4. The dams cause sustained high-water temperatures during the summer and early fall that weaken or kill migrating fish.
5. The dams kill adult fish returning to their spawning grounds.
6. The dams increase, on average 10-times, the amount of time it takes juvenile salmon to reach the ocean; this increases their exposure to predators and causes a mismatch between timing of ocean entry and the process of smoltification (the physiological change juvenile salmon and steelhead undergo to prepare for a saltwater environment).
7. The dams diminish the food supply for juvenile fish by inundating river habitat that produces food.
8. The reservoirs behind the dams provide habitat for both invasive and native predatory fish and make juvenile fish easy targets for predatory birds.