There are almost 80,000 dams in the US. In nearly every case, they isolate fish populations, collect sediment, alter water temperatures, lower oxygen levels, and disrupt flow cycles. The riverine habitat is completely changed or destroyed.
The good news is that rivers can recover, and quickly, if given the chance. Dam removals across the country are showing us how the environment reacts when the dam is taken out. Natural flow conditions develop quickly after the majority of the sediment is removed and species diversity often doubles.