Roosevelt Dam in Arizona.

Cheoah Dam on the Little Tennessee River in Graham and Swain counties, North Carolina.

Cheoah Dam on the Little Tennessee River in Graham and Swain counties, North Carolina.

Cheoah Dam on the Little Tennessee River in Graham and Swain counties, North Carolina.

Cheoah Dam on the Little Tennessee River in Graham and Swain counties, North Carolina.

Norris Dam on the Clinch River in Tennessee.

Norris Dam on the Clinch River in Tennessee.

Norris Dam on the Clinch River in Tennessee.

Construction and equipment on the Hoover Dam.

Beaver dam in Colorado.

Wilson Dam at Muscle Shoals, Alabama.

Interior of Wilson Dam at Muscle Shoals, Alabama.