resevoir

Hoover Dam, a concrete arch-gravity dam in the Black Canyon of the Colorado River on the border between the US states of Arizona and Nevada. Hoover Dam ,finished in 1936, impounds Lake Mead, the largest reservoir in the United States by volume. The dam's generators provide power for public and private utilities in Nevada, Arizona, and California. Hoover Dam is a major tourist attraction; nearly a million people tour the dam each year.

Joe Klamar/AFP

The sun rises over the Hoover Dam, a concrete arch-gravity dam in the Black Canyon of the Colorado River on the border between the US states of Arizona and Nevada. The Hoover Dam was finished in 1936 and impounds Lake Mead, the largest reservoir in theUS by volume.

Pakistani women, wash their laundry at a water reservoir, on the outskirts of Islamabad, Pakistan, Thursday, March 20, 2014. The United Nations has proclaimed that March 20 is the International Day of Happiness.

Muhammed Muheisen/AP

Pakistani women, wash their laundry at a water reservoir, on the outskirts of Islamabad, Pakistan. The United Nations has proclaimed that March 20 is the International Day of Happiness.