Because beavers build their stick-and-mud dams in streams flowing through shallow valleys, the flooded area becomes freshwater wetlands. Such wetlands are rated by ecologists and economists as the land’s most beneficial ecosystem.* Because beaver dams create mini-reservoirs that keep water on the land longer, they can alleviate both droughts and regional floods.
Beavers build leaky dams that slow the flow of streams, creating quiet water nurseries for fish and many other organisms. About half of the rare species require wetlands during their life cycles, according to US EPA. Slowing the flow also allows time for wetland microorganisms to detoxify pollutants, such as pesticides. Beaver dams accentuate the normal filtering function of wetlands by collecting silt, and there can be 90% less sediment in the water downstream. Such water cleansing results in healthier downstream habitats, and less costly treatment is needed at plants to produce drinking water for people.