Big Dams: Boon or Bane?

Dams help control floods. They store water to irrigate fields and supply cities. They harness energy that generates electricity without consuming fossil fuels.

Conversely, dams displace communities, obliterate natural habitats, interrupt sediment flows, and block migratory fish.

This story examines the mixed blessing of big dams—first by visiting some of the world's largest, then by exploring dams as hazards and examining two rivers that have been radically altered by dam-building programs.

The size of a dam can be measured several ways, among them the volume of the dam structure itself, the size of the body of water it impounds, and the amount of hydroelectric power it produces. Below is a sampling of big dams in each of these categories.

Although dam failures are rare, they can be catastrophic. Large populations continue to be at risk from aging and poorly built dams.

Hundreds of the world's rivers have been dammed at multiple locations. Among the more famous are the Columbia River in the United States and Canada, and the Mekong River in Southeast Asia.

Explore big dams worldwide

Support these organizations

International Rivers protects rivers and defends the rights of communities that depend on them.

American Rivers protects wild rivers, restores damaged rivers and conserves clean water for people and nature.