What dams do and do not do

Dams do not save rivers.

Yard signs in town would have you think otherwise, but they might as well proclaim that pigs can fly.

Here’s what dams do: Dams alter rivers. Whether the dam is made by a family of beavers or a crew of humans, the effect is that flowing water is obstructed. The water behind the obstruction becomes a pool. With little movement of water, two things happen in the aquatic environment: the amount of dissolved oxygen decreases, and silt builds up behind the dam. This changes the living conditions for aquatic wildlife and plants. As aquatic life changes, the terrestrial life that depends on aquatic life changes as well.

Dams prevent aquatic animals from moving up and downstream. This affects a host of animals, particularly fish and freshwater mussels that require movement up and down the river to reproduce. By blocking their movement, dams decrease the reproductive success of beneficial native aquatic wildlife.

Here’s what dams do not do: They do not last forever. Beaver dams naturally give way after a while. Humans, however, tend to want man-made dams to remain static. If man-made dams are not maintained or repaired, they will fail over time. The failure of a man-made dam has serious (and sometimes fatal) repercussions for humans living along the river.

Keeping a man-made dam does not save a river. It saves a human vision of a river. The river in that vision is less healthy, less diverse, and less stable than a free-flowing river.

Valerie Blaine

St. Charles