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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.

Full Article

  • 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 Gulf of California (Sea of Cortez), 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 246,000 square miles (about 637,000square kilometers). This drainage area includes portions of seven states in the US: 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 part 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 with a substantial amount 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 Rims) 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 the Hoover Dam, the Colorado River continues south. Along the California-Arizona stretch of the river, four additional dams function to divert water for agricultural irrigation and municipal water uses and to form reservoirs for recreational purposes.

Historically, 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, except during occasional restoration pulse flows under binational agreements. 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 one of the largest irrigation canals 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. 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 richest areas for plants and animals along the Colorado River. Above and below the walls of the Grand Canyon, there are 90 species of mammals, nearly 50 species of reptiles, about 10 amphibians, 25 species of fish, and over 400 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. Summer 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, coyotes, and bighorn sheep. More than400 species of birds inhabit this region, including the red-tailed hawk, the golden eagle, the peregrine falcon, and the critically endangered California condor. The Colorado River Basin harbors thirty native species of fish. Fourteen of these species are endemic (found nowhere else on Earth), and some are endangered, such as the 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 Parks and Wildlife, and the Utah Division of Wildlife Resources, 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, along with subsequent agreements and ongoing post-2026 operational negotiations. Nearly 70 to 80 percent of all 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 sandbars 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 ongoing climate change.

The Western United States, including the area around the Colorado River, has been suffering through severe drought conditions since 2000. At the same time, the population of the states that depend on the river for their water has increased. Nearly forty million people depend upon the Colorado for their water. Since 2000, the river level has been steadily decreasing, as have 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, and 30 percent in 2025. Since reaching its high-water mark in 1983, the lake level has dropped 170 feet.


Bibliography

Bank, David. “As the Colorado River Runs Dry, Impact Investors Seek Water Solutions.” HuffPost, 30 Sept. 2015, www.huffpost.com/entry/as-the-colorado-river-run_b_8215980. Accessed 4 Mar. 2026.

Benke, Arthur C., and Colbert E. Cushing, editors. Field Guide to Rivers of North America. Elsevier, 2010.

“Colorado River Basin Studies.” U.S. Geological Survey, www.usgs.gov/centers/utah-water-science-center/science/colorado-river-basin-studies. Accessed 2 Mar. 2026.

Cushing, Colbert E., et al., editors. River and Stream Ecosystems of the World. U of California P, 2006.

Davis, Tony. “Study: Colorado River Shortage Could Hit Arizona Hard.” Arizona Daily Star, 30 Sept. 2016, tucson.com/news/science/environment/study-colorado-river-shortage-could-hit-arizona-hard/article_18e2c791-99fd-576f-b4cc-708b6e60bc68.html. Accessed 4 Mar. 2026.

Fradkin, Philip L. A River No More: The Colorado River and the West. U of California P, 1996.

Nandi, Kathakali. “Water Levels in Lake Mead Stay Low Even As California Reservoirs Overflow.” edhat, 5 Jan. 2026, www.edhat.com/news/water-levels-in-lake-mead-stay-low-even-as-california-reservoirs-overflow/. Accessed 4 Mar. 2026.

Powell, Alvin. “Lessons Emerge as Seven Thirsty States War over Colorado River Water.” The Harvard Gazette, 14 Feb. 2023, news.harvard.edu/gazette/story/2023/02/colorado-river-crisis-explained/. Accessed 3 Mar. 2026.

Rice, Matt. “Colorado River Named America’s #1 Most Endangered River of 2022.” American Rivers, 18 Apr. 2022, www.americanrivers.org/media-item/colorado-river-named-americas-1-most-endangered-river-of-2022/. Accessed 3 Mar. 2026.

Rocchio, Laura E. P. “Meat of the Matter: Colorado River Over-Consumed.” NASA Science, 30 Apr. 2024, science.nasa.gov/missions/landsat/meat-of-the-matter-colorado-river-over-consumed. Accessed 3 Mar. 2026.

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.” The Denver Post, 5 Dec. 2022, www.denverpost.com/2022/07/21/colorado-river-drought-water-crisis-west/. Accessed 3 Mar. 2026.

“Wildlife – Grand Canyon National Park (U.S. National Park Service).” National Park Service, 2016, www.nps.gov/grca/learn/nature/wildlife.htm. Accessed 3 Mar. 2026.

Full Article

  • 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 Gulf of California (Sea of Cortez), 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 246,000 square miles (about 637,000square kilometers). This drainage area includes portions of seven states in the US: 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 part 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 with a substantial amount 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 Rims) 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 the Hoover Dam, the Colorado River continues south. Along the California-Arizona stretch of the river, four additional dams function to divert water for agricultural irrigation and municipal water uses and to form reservoirs for recreational purposes.

Historically, 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, except during occasional restoration pulse flows under binational agreements. 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 one of the largest irrigation canals 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. 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 richest areas for plants and animals along the Colorado River. Above and below the walls of the Grand Canyon, there are 90 species of mammals, nearly 50 species of reptiles, about 10 amphibians, 25 species of fish, and over 400 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. Summer 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, coyotes, and bighorn sheep. More than400 species of birds inhabit this region, including the red-tailed hawk, the golden eagle, the peregrine falcon, and the critically endangered California condor. The Colorado River Basin harbors thirty native species of fish. Fourteen of these species are endemic (found nowhere else on Earth), and some are endangered, such as the 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 Parks and Wildlife, and the Utah Division of Wildlife Resources, 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, along with subsequent agreements and ongoing post-2026 operational negotiations. Nearly 70 to 80 percent of all 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 sandbars 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 ongoing climate change.

The Western United States, including the area around the Colorado River, has been suffering through severe drought conditions since 2000. At the same time, the population of the states that depend on the river for their water has increased. Nearly forty million people depend upon the Colorado for their water. Since 2000, the river level has been steadily decreasing, as have 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, and 30 percent in 2025. Since reaching its high-water mark in 1983, the lake level has dropped 170 feet.


Bibliography

Bank, David. “As the Colorado River Runs Dry, Impact Investors Seek Water Solutions.” HuffPost, 30 Sept. 2015, www.huffpost.com/entry/as-the-colorado-river-run_b_8215980. Accessed 4 Mar. 2026.

Benke, Arthur C., and Colbert E. Cushing, editors. Field Guide to Rivers of North America. Elsevier, 2010.

“Colorado River Basin Studies.” U.S. Geological Survey, www.usgs.gov/centers/utah-water-science-center/science/colorado-river-basin-studies. Accessed 2 Mar. 2026.

Cushing, Colbert E., et al., editors. River and Stream Ecosystems of the World. U of California P, 2006.

Davis, Tony. “Study: Colorado River Shortage Could Hit Arizona Hard.” Arizona Daily Star, 30 Sept. 2016, tucson.com/news/science/environment/study-colorado-river-shortage-could-hit-arizona-hard/article_18e2c791-99fd-576f-b4cc-708b6e60bc68.html. Accessed 4 Mar. 2026.

Fradkin, Philip L. A River No More: The Colorado River and the West. U of California P, 1996.

Nandi, Kathakali. “Water Levels in Lake Mead Stay Low Even As California Reservoirs Overflow.” edhat, 5 Jan. 2026, www.edhat.com/news/water-levels-in-lake-mead-stay-low-even-as-california-reservoirs-overflow/. Accessed 4 Mar. 2026.

Powell, Alvin. “Lessons Emerge as Seven Thirsty States War over Colorado River Water.” The Harvard Gazette, 14 Feb. 2023, news.harvard.edu/gazette/story/2023/02/colorado-river-crisis-explained/. Accessed 3 Mar. 2026.

Rice, Matt. “Colorado River Named America’s #1 Most Endangered River of 2022.” American Rivers, 18 Apr. 2022, www.americanrivers.org/media-item/colorado-river-named-americas-1-most-endangered-river-of-2022/. Accessed 3 Mar. 2026.

Rocchio, Laura E. P. “Meat of the Matter: Colorado River Over-Consumed.” NASA Science, 30 Apr. 2024, science.nasa.gov/missions/landsat/meat-of-the-matter-colorado-river-over-consumed. Accessed 3 Mar. 2026.

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.” The Denver Post, 5 Dec. 2022, www.denverpost.com/2022/07/21/colorado-river-drought-water-crisis-west/. Accessed 3 Mar. 2026.

“Wildlife – Grand Canyon National Park (U.S. National Park Service).” National Park Service, 2016, www.nps.gov/grca/learn/nature/wildlife.htm. Accessed 3 Mar. 2026.

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