Colorado River
The Colorado River, stretching approximately 1,450 miles from the Rocky Mountains to the Pacific Ocean, serves as a vital freshwater resource for the southwestern United States and northwestern Mexico. This river is essential for agricultural irrigation, drinking water, recreation, and industrial uses, with the majority of its flow originating from snowmelt in the Rockies. The river traverses diverse landscapes, including the iconic Grand Canyon, and is fed by numerous tributaries, which collectively drain a vast watershed of about 200,000 square miles across multiple states.
Management of the Colorado River is crucial for sustaining both human communities and the wildlife that depend on its ecosystems. However, the river faces significant challenges, including overuse of its water for agriculture and urban supply, leading to diminished flow reaching its delta in Mexico. Notable environmental concerns include the impact of dams on the river's ecology, which have disrupted natural flooding cycles necessary for habitat maintenance.
As climate conditions continue to evolve, the Colorado River, relied upon by approximately 40 million people, is increasingly threatened by drought and declining water levels in its reservoirs, such as Lake Mead. These developments raise important questions about the river's future and the sustainability of its vital resources for diverse populations in the region.
Colorado River
Category: Inland Aquatic Biomes
Geographic Location: North America
Summary: The Colorado River is the main freshwater artery in the southwestern United States and northwestern Mexico.
Rising in the Rocky Mountains and passing through great expanses of arid land on its way to the Pacific Ocean, the Colorado River is the main freshwater artery in the southwestern United States and northwestern Mexico. It is a critical water resource for the people and wildlife in this part of the world. Most of the water is used for agricultural irrigation, but water diverted from the river is also used for drinking as well as for recreation and industry. Reservoirs produced by dams on the river and its tributaries provide long-term water storage for communities and farms along the river. Management of this precious resource must include provisions for wildlife sustained by the river, as well as for the inhabitants of Mexico, who receive only a small portion of all initial runoff.
Geography
The Colorado River is approximately 1,450 miles (2,300 kilometers) in length, flowing mostly west and south, draining a large portion of the arid regions of the western slopes of the Rocky Mountain range. Most of the water that courses through the Colorado River canyons and its tributaries is from snowmelt. The watershed of the Colorado River is extremely large, encompassing approximately 200,000 square miles (50,000 square kilometers). This drainage area includes portions of seven of the United States—Wyoming, Colorado, Utah, New Mexico, Nevada, Arizona, and California—and two states of Mexico: Sonora and Baja California. For 17 miles (27 kilometers), the Colorado River makes up the boundary between the United States (in Arizona) and Mexico.
The Colorado River originates from the Continental Divide at La Poudre Pass in Rocky Mountain National Park, Colorado, approximately 25 miles (40 kilometers) north of Lake Granby. The elevation at this location is 10,000 feet (3,000 meters). As the river leaves Rocky Mountain National Park, it empties first into Shadow Mountain Lake and then into Lake Granby. These lakes are parts of the Colorado-Big Thompson Project, a large water storage and delivery system that diverts water from the Colorado River to provide water for agricultural and municipal uses for the northern Front Range and the plains of Colorado.
The Roaring Fork River empties into the Colorado at the city of Glenwood Springs; then the Colorado is joined by the Gunnison River at Grand Junction. Both the Roaring Fork and Gunnison Rivers are swift-flowing major streams that provide the Colorado massive amounts of water. After this junction, the Colorado flows through Ruby Canyon and crosses into Utah and into Westwater Canyon. The river continues on through Utah and Arizona, through more canyons; is joined by additional rivers, such as the Dolores and Green Rivers; and then flows into Lake Powell, which is formed by the Glen Canyon Dam in Utah.
In Arizona, at the southern end of Marble Canyon, the Little Colorado River empties into the Colorado, and the river enters the Grand Canyon and Grand Canyon National Park. The Grand Canyon is 217 miles (350 kilometers) in length, and the distances between the upper cliffs (South and North Ridges) vary from 4 to 20 miles (6 to 32 kilometers). The walls of the Grand Canyon are 4,000 to 6,000 feet (1,200 to 1,800 meters) high, dropping in successive escarpments of 500 to 1,600 feet (150 to 500 meters). The rocks are striated in columns of striking colors, layered in an abundance of fossils, and create one of the most exposed and explicit geologic formations on the planet.
In Nevada, the Hoover Dam, which was constructed during the Great Depression, forms Lake Mead, which serves as a popular recreation area as well as the major water supply for most of the Las Vegas metropolitan area. From Hoover Dam, the Colorado River continues south. Along the California-Arizona stretch of the river, four additional dams currently function to divert water for agricultural irrigation and municipal water uses, and to form reservoirs for recreational purposes.
Formerly, the river emptied into the Gulf of California between the Baja California peninsula and the mainland of Mexico, but it no longer reaches the Gulf of California on a regular basis. This is due to the large number of diversions of water from the river for agricultural irrigation, use of the river for urban water supplies, and significant evaporation losses from reservoirs produced by damming the river. More than twenty major dam projects have been completed on the Colorado River and its tributaries.
The lower course of the Colorado River forms the border between the Mexican state of Sonora on the mainland and the state of Baja California on the Baja California peninsula. The river at this location is either dry or a small stream for most of the year, due to the numerous diversions upstream, and especially due to the diversion of water for agricultural irrigation in the Imperial Valley of California. The All-American Canal is the major water supply route from the Colorado River to the Imperial Valley; the water is used to irrigate orchards and row crops in the valley. This canal is the largest irrigation canal in the world; it carries a volume of water that ranges from 15,000 to 26,000 cubic feet (425 to 735 cubic meters) per second. Before the middle of the twentieth century, the Colorado River delta was a diverse estuarine ecosystem. At present, it is mostly dried up, but the river still continues to be an important ecological estuary.
Flora and Fauna
The Grand Canyon is one of the richer areas for plants and animals along the Colorado River. Above and below the walls of the Grand Canyon, there are 75 species of mammals, 50 species of reptiles and amphibians, 25 species of fish, and over 300 species of birds. On the canyon rims at elevations above 7,000 feet (2,000 meters), ponderosa pine is the dominant tree. Douglas fir, blue spruce, and Gambel oak are other common trees here. Below this elevation, pinyon pine and Utah juniper are the dominant trees. The trees are interspersed with drought-resistant shrubs like cliffrose, fernbush, and serviceberry. Warm, sunny areas along the rim may be home to desert plants such as yucca, sage, and various cacti.
Down in the canyon itself, it is like another world. The temperature within the inner canyon can be as much as 30 degrees F (18 degrees C) higher than temperatures on the rim. Summertime highs along the Colorado River can reach 120 degrees F (49 degrees C). Much of the inner canyon is considered desert, excluding the areas along the river and tributary streams which have rich riparian habitat. Much of the vegetation in the inner canyon is typical of that found in deserts to the south: cacti and drought-resistant shrubs. Riparian plants include thickets of willow and tamarisk.
Prominent mammal species in the Colorado canyons include several types of squirrels, mule deer, elk, and coyote, and bighorn sheep. Around 90 species of birds inhabit this region, including the red-tailed hawk, the golden eagle, the peregrine falcon, and the endangered California condor. The Colorado River Basin harbors 14 native species of fish. Four of these species are endemic (found nowhere else on Earth) and endangered: Colorado pike minnow, razorback sucker, bonytail chub, and humpback chub. The Upper Colorado River Endangered Fish Recovery Program is an effort by the US Fish and Wildlife Service, in cooperation with the Arizona Game and Fish Department, the Colorado Division of Wildlife, and the Utah Department of Wildlife, to rebuild the populations of these endangered fish species.
The Colorado River is a critical water resource for the people who live in the arid southwestern United States and Mexico. The water from this river is essential for irrigation, drinking water, and other uses by people throughout the region. Unfortunately, Mexico receives little of the enormous quantity of water that surges through parts of the Colorado canyons.
Allocation of the water in the Colorado River is determined by the Colorado River Compact, an agreement signed in 1922 by seven states in the Colorado River basin. Nearly 90 percent of all of the water diverted from the Colorado River is used for irrigation purposes in the United States. Several cities—such as Phoenix and Tucson (the Central Arizona Project), Los Angeles and San Bernardino (Colorado River Aqueduct), Las Vegas, and San Diego—have canals or aqueducts that run from the Colorado River to these major urban centers.
The large number of dams on the Colorado River has had negative environmental effects on the ecology and hydrology of the river. The dams have prevented much of the seasonal flooding normal to the river that would clean the river of debris. The lack of flooding has also caused erosion of sand bars in the Grand Canyon, which are essential for a variety of wildlife in that region of the river. The diversion of water to irrigate farmlands and to supply large cities has taken a huge toll on the quantity of water available to existing habitats. The Colorado River and its wildlife face the challenges of water loss due to overuse, drought, and future climate changes.
The Western united States, including the area around the Colorado River, has been suffering through sever drought conditions since 2000. At the same time, the population of the states that depend on the river for their water has increased. An estimated forty million people depended upon the Colorado for their water in 2022. Since 2000, the river level has been steadily decreasing, as has the water levels of the reservoir lakes formed by the dams along its route. For example, Lake Mead was at 95 percent capacity in 2000; by 2022, the lake was at 27 percent capacity. Since reaching its high-water mark in 1983, the lake level has dropped 170 feet.
Bibliography
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Benke, Arthur C. and Colbert E. Cushing, eds. Field Guide to Rivers of North America. Boston: Elsevier, 2010.
Cushing, Colbert E., Kenneth W. Cummins, and G. Wayne Minshall, eds. River and Stream Ecosystems of the World. Berkeley: U of California P, 2006.
Davis, Tony. "Study: Colorado River Shortage Could Hit Arizona Hard." Arizona Daily Star. Arizona Daily Star, 12 Sept. 2015.
Fradkin, Philip L. A River No More: The Colorado River and the West. Berkeley: U of California P, 1996.
Swanson, Conrad. "The West’s Most Important Water Supply Is Drying Up. Soon, Life for 40 Million People Who Depend on the Colorado River Will Change."Denver Post, 21 Jul. 2022, www.denverpost.com/2022/07/21/colorado-river-drought-water-crisis-west/. Accessed 1 Aug. 2022.
Trotter, Jim. "ASU Study Details Economic Impact of Colorado River on Basin States." Rocky Mountain PBS I-News. Rocky Mountain PBS I-News, 25 Sept. 2015.