What Are the Positive and Negative Effects of Dams?

Building dams offers the positive results of inexpensive energy, increased recreation opportunity and flood control. However, these results are not without negative impacts, as dams interfere with the ecological system and eliminate the benefits of flooding on farmlands downstream.

In the Pacific Northwest of the United States, electricity is cheap, largely due to the resources provided by the Bonneville Power Administration. Water from behind the Bonneville turns the turbines to create large amounts of power. The lakes created by dams provide opportunities for many different types of water sports, including fishing, boating and swimming. These dams have saved millions of dollars and thousands of lives by giving humans control over floods that once destroyed property downstream.

Dams have a negative effect on aquatic ecosystems. Fish, such as salmon that depend on their ability to move from the ocean upstream for spawning, suffer when dams block their path to their breeding grounds. Scientific studies on the Klamath River indicate the positive benefits removing dams along the river include restoration of endangered salmon and the improvement in trout habitat. The positive benefits of dam removal outweigh the negative impacts of leaving them in place. When rich floodplains no longer receive their annual deposits of silt from floods, they become less fertile. Dams that hold back floodwaters and then open floodgates also increase erosion downstream due to the surge of water.