The Colorado River flowing into the Gulf of California, also referred to as the Sea of Cortés, is pictured in this satellite image. The delta is located between the two Mexican states of Baja California (left) and Sonora (right). Known for its incredible canyons, whitewater rapids, and eleven U.S. National Parks, the Colorado River and its tributaries are a vital source of water for 40 million people. The river stretches for about 2,330 km and, due to its capacity, large basins have been built for hydroelectric plants in its lower course, but the massive collection of its water for irrigation in the Imperial Valley, and civil uses, has drained its low course (in Mexico) to such an extent that there are years when the river fails to reach the sea. The Upper Gulf of California and Colorado River Delta were registered by UNESCO as a Biosphere Nature reserve. A large portion of the Biosphere reserve has been included in the RAMSAR list of wetlands of international importance.