Query: Last year, though, was a wet one on the Rio Grande, with a strong snowpack in the winter of 2016-17 that allowed the conservancy district to store water in upstream reservoirs.

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Glen Canyon Dam <=SEP=> Glen Canyon Dam is a concrete arch-gravity dam on the Colorado River in northern Arizona , United States , near the town of Page . The 710 ft high dam was built by the U.S. Bureau of Reclamation ( USBR ) from 1956 to 1966 and forms Lake Powell , one of the largest man-made reservoirs in the U.S. with a capacity of 27 million acre feet ( 33 km3 ) . The dam is named for Glen Canyon , a series of deep sandstone gorges now flooded by the reservoir ; Lake Powell is named for John Wesley Powell , who in 1869 led the first expedition to traverse the Colorado 's Grand Canyon by boat .   A dam in Glen Canyon was studied as early as 1924 , but these plans were initially dropped in favor of a dam in Black Canyon ( the Hoover Dam , completed in 1936 ) . By the 1950s , due to rapid population growth in the seven U.S. and two Mexican states comprising the Colorado River Basin , the Bureau of Reclamation deemed the construction of additional reservoirs necessary . However , the USBR faced opposition when it proposed the Echo Park Dam in Utah 's Dinosaur National Monument , which the nascent environmental movement saw as a legal threat to the status of protected lands . After a long fight , the USBR agreed not to build the dam in Dinosaur , but only if the environmentalists did not oppose the proposed dam in Glen Canyon .   Since first filling to capacity in 1980 , Lake Powell water levels have fluctuated greatly depending on water demand and annual runoff . Operation of Glen Canyon Dam helps ensure an equitable distribution of water between the states of the Upper Colorado River Basin ( Colorado , Wyoming , and most of New Mexico and Utah ) and the Lower Basin ( California , Nevada and most of Arizona ) . During years of drought , Glen Canyon guarantees a water delivery to the Lower Basin states , without the need for rationing in the Upper Basin . In wet years , it captures extra runoff for future use . The dam is also a major source of hydroelectricity , averaging over 4 billion kilowatt hours per year . The long and winding Lake Powell , known for its scenic beauty and recreational opportunities including houseboating , fishing and water-skiing , attracts millions of tourists each year to the Glen Canyon National Recreation Area .   In addition to its flooding of the scenic Glen Canyon , the dam 's economic justification was highly questioned ; with what critics saw as unnecessary damage to the wilderness , it became `` a catalyst for the modern environmental movement , '' and was one of the last dams of its size to be built in the United States . The dam has been criticized for the huge evaporative losses from Lake Powell and its heavy impact on the ecology of the Grand Canyon , which lies downstream ; environmental groups continue to advocate for the dam 's removal . Water managers and utilities state that the dam is a major source of renewable energy and provides a vital defense against severe droughts .

Colorado River <=SEP=> The Colorado River is one of the principal rivers of the Southwestern United States and northern Mexico ( the other being the Rio Grande ) . The 1450 mi river drains an expansive , arid watershed that encompasses parts of seven U.S. and two Mexican states . Starting in the central Rocky Mountains in the U.S. , the river flows generally southwest across the Colorado Plateau and through the Grand Canyon before reaching Lake Mead on the Arizona -- Nevada border , where it turns south toward the international border . After entering Mexico , the Colorado approaches the mostly dry Colorado River Delta at the tip of the Gulf of California between Baja California and Sonora .   Known for its dramatic canyons , whitewater rapids , and eleven U.S. National Parks , the Colorado River system is a vital source of water for 40 million people in southwestern North America . The river and its tributaries are controlled by an extensive system of dams , reservoirs , and aqueducts , which in most years divert its entire flow for agricultural irrigation and domestic water supply . Its large flow and steep gradient are used for generating hydroelectric power , and its major dams regulate peaking power demands in much of the Intermountain West . Intensive water consumption has dried up the lower 100 mi of the river , which has rarely reached the sea since the 1960s .   Beginning with small bands of nomadic hunter-gatherers , Native Americans have inhabited the Colorado River basin for at least 8,000 years . Between 2,000 and 1,000 years ago , the river and its tributaries fostered large agricultural civilizations -- some of the most sophisticated indigenous cultures in North America -- which eventually faded due to a combination of severe drought and poor land use practices . Most native peoples that inhabit the basin today are descended from other groups that settled in the region beginning about 1,000 years ago . Europeans first entered the Colorado Basin in the 16th century , when explorers from Spain began mapping and claiming the area , which later became part of Mexico upon its independence in 1821 . Early contact between Europeans and Native Americans was generally limited to the fur trade in the headwaters and sporadic trade interactions along the lower river .   After most of the Colorado River basin became part of the U.S. in 1846 , the bulk of the river 's course was still the subject of myths and speculation . Several expeditions charted the Colorado in the mid-19th century -- one of which , led by John Wesley Powell , was the first to run the rapids of the Grand Canyon . American explorers collected valuable information that was later used to develop the river for navigation and water supply . Large-scale settlement of the lower basin began in the mid - to late-19th century , with steamboats providing transportation from the Gulf of California to landings along the river that linked to wagon roads to the interior . Lesser numbers settled in the upper basin , which was the scene of major gold strikes in the 1860s and 1870s .   Large engineering works began around the start of the 20th century , with major guidelines established in a series of international and U.S. interstate treaties known as the `` Law of the River '' . The U.S. federal government was the main driving force behind the construction of dams and aqueducts , although many state and local water agencies were also involved . Most of the major dams were built between 1910 and 1970 ; the system keystone , Hoover Dam , was completed in 1935 . The Colorado is now considered among the most controlled and litigated rivers in the world , with every drop of its water fully allocated .   The environmental movement in the American Southwest has opposed the damming and diversion of the Colorado River system because of detrimental effects on the ecology and natural beauty of the river and its tributaries . During the construction of Glen Canyon Dam , environmental organizations vowed to block any further development of the river , and a number of later dam and aqueduct proposals were defeated by citizen opposition . As demands for Colorado River water continue to rise , the level of human development and control of the river continues to generate controversy .