Spilling smolts over the spillways is a beneficial procedure, however spilled water does not produce power. The aluminum and navigation industries oppose spill. Natural river migration advocates support spill. The four dams on the lower Snake River may have more impact on the salmon than the lower dams on the Columbia River. Natural river migration advocates have proposed decomissioning the lower Snake River Dams.
Opponents argue that the dams are essential for navigation and hydropower generation.
There are many obvious as well as subtle changes that occur. Plant and animal communities adapted to still, warm water environments will replace those adapted to colder free flowing rivers. Fundamental changes in productivity, food chains and nutrient cycling will occur. If you are fortunate to live near a free flowing river, you might pose this question in terms of the predicted impacts of constructing a dam or dams on your river. Another way to approach this concept would be to predict the impact of removing dams from a river that is presently obstructed by dams.