Water in Colorado

Water has profoundly shaped Colorado’s past and will play a vital role in its future. The resource is essential to the state’s agriculture, cities, industries, energy supply, and environment. Furthermore, eighteen other states and parts of Mexico rely on waters from the mountains of Colorado, known as the Headwaters State. Tens of millions of people and billions of dollars of economic activity between California and the Mississippi River depend on water that begins in Colorado’s mountains. Scarcity of this vital resource has created controversy and conflict, but water challenges have also led to cooperation and collaboration.

Geography, Weather, and Climate

Weather in Colorado can differ dramatically from year to year. Severe droughts like the Dust Bowl of the 1930s and the historic dryness of 2012 alternate with destructive deluges, including the Big Thompson Flood of 1976, which killed more than 140 people, and the catastrophic northern Front Range flooding of 2013.

The state’s diverse geography ranges from under 3,400 feet above sea level at a low point on the eastern plains to Rocky Mountain summits that soar above 14,000 feet, creating a climate marked by stark regional differences. Clouds tend to pass over the deserts and canyons of western Colorado. They dump their moisture on the high peaks, and the eastern plains lie in the dry rain shadow cast by this mountain wall.

Blizzards bury the Rocky Mountains in winter, creating reservoirs of snowpack. In spring, the snowpack melts, and water runs down from the peaks to the plains and valleys, supporting ecosystems and recreation and allowing cities and farms to thrive. The state’s rivers swell with snowmelt in spring and early summer; in the late summer and fall, their flow diminishes as snow melts away. Dams capture spring runoff in reservoirs so the stored water can be distributed during dry months and years, smoothing out natural fluctuations in the water supply. Diversion systems move water from places where precipitation is abundant to where it is scarce, replenishing the state’s river basins.

The Continental Divide, which separates waters that flow to the Pacific Ocean from those that enter the Atlantic, splits the state into the Western and Eastern Slopes. Some 80 percent of the state’s water originates in Western Slope rivers, but more than 80 percent of Colorado’s population lives on the Eastern Slope. This mismatch between water supply and population lies at the heart of many of the state’s long-running water conflicts and hard-won compromises.

Four of the most important rivers in the American West begin in the snows of Colorado’s Great Divide. The South Platte, Arkansas, and Rio Grande run down the eastern side of the divide in the Atlantic watershed. The Colorado River runs west to the Pacific, but human engineering redirects a portion of the Colorado’s flow across the Continental Divide to the farms and cities of the Front Range.

Water History

From the Ancestral Puebloans who inhabited Mesa Verde until the late 1200s to the Ute, Navajo, Arapaho, and Cheyenne, who lived in the region until white settlement in the nineteenth century, the survival of the first Coloradans depended on efficient use of scarce water supplies. Explorers, mountain men, and mapmakers relied on rivers as avenues for travel that provided shelter, game, and lifesaving stores of water amid the harsh landscape of the High Plains, which Major Stephen Long labeled on an early map as the “Great American Desert.” The San Luis People’s Ditch, an irrigation channel established in the San Luis Valley in 1852 and based on a water management system of Spanish origin, holds the earliest water right in continuous use in Colorado.

Beginning in 1858, the Colorado Gold Rush helped lay the foundation for the legal system governing Colorado’s water, which was essential for mining. To manage water disputes, miners adopted the doctrine of prior appropriation—the principle that the first person to put water to use has the legal right to continue using that same amount of water. Gold prospectors were followed by homesteaders, who launched irrigated agriculture on Colorado’s semiarid eastern plains, leading to clashes over the use of water sources. These conflicts resulted in landmark court cases that established a statewide system of water law based on prior appropriation. Colorado water law helped shape the legal landscape of the American West and paved the way for the development of water-scarce lands.

Irrigation ditches transformed drought-plagued prairie into productive cropland and pastureland. Technological innovations allowed farming and ranching to flourish throughout the state, giving rise to an industry that forms a vital part of Colorado’s economy. Today, agriculture accounts for approximately 86 percent of all surface and groundwater use in the state. But as population grows, pressure to move water from agriculture to cities increases.

Denver Water, the state’s oldest and largest water utility, was established in 1918 to ensure a stable water supply for the growing metropolis. Denver Water and other entities constructed engineering works to dam rivers and divert flow from the Western Slope across the Continental Divide to the Eastern Slope, despite opposition from western Colorado, which wanted water to remain in its rivers to support the area’s agriculture and future growth. The impact of these transmountain diversions became a point of contention, and western states battled among themselves over rivers born in the snows of Colorado.

The Colorado River Compact of 1922 resulted from negotiations led by Colorado attorney Delph Carpenter. This historic agreement prevented endless and paralyzing litigation by dividing the flow of the most important river in the American Southwest among states in the Colorado River Basin.

The year 1937 was a watershed in Colorado history. A hard-won compromise between the Eastern and Western Slopes cleared the way for the state to develop some of its water resources allocated from the Colorado River Compact. Additionally, the establishment of a framework to manage water through organizations such as the Colorado Water Conservation Board, the Colorado River Water Conservation District, and the Northern Colorado Water Conservancy District set the stage for the Colorado–Big Thompson Project. This monumental diversion system financed and built by the federal government redirected flow from the Colorado River headwaters across the Great Divide to the plains of northeastern Colorado. Other major dams and diversions built by the federal government followed.

Congressman Wayne Aspinall advocated for water development in Colorado at the national level from the mid-1950s to the early 1970s. Water projects he championed brought benefits as well as controversy. The modern environmental movement in America was born in large part during battles over water projects supported by Representative Aspinall, most notably the Echo Park Dam proposed in Dinosaur National Monument in the 1950s.

The environmental movement gained momentum in the 1960s and 1970s as society’s changing values led to balancing water development against protecting rivers’ ecological health. Federal legislation such as the Wilderness Act, the Clean Water Act, and the Endangered Species Act reflected this shift. Also beginning in the 1960s, Colorado passed legislation to manage some of the state’s underground water supplies based on their finite quantity and their connection to rivers.

In 1990, the Environmental Protection Agency vetoed Denver Water’s proposed Two Forks Dam, forcing Denver and its suburbs to rely largely on conservation to make up for the metropolitan area’s water supply shortfall. In the wake of the dam veto, Denver Water began working with the Western Slope to develop mutually acceptable solutions to the water challenges that have divided the state throughout much of its history.

Recent decades have seen increased collaboration between water interests traditionally at odds with each other. In 2013 more than forty partners—including Denver Water, Mesa County and Grand Valley Irrigation Districts; the towns of Breckenridge, Dillon, Frisco, and Silverthorne; and the Colorado River Conservation District—approved the Colorado River Cooperative Agreement. The historic agreement brought together myriad interests under a singular vision for the future of water in the state and marked a turning point in clashes between Denver Water and the Western Slope. Despite the agreement, water conflicts are likely to continue as the state faces increasing demand on a limited resource for which there is no substitute.

Future Water Challenges

Colorado’s water use is constrained by interstate agreements such as the Colorado River Compact. But the state’s population is projected to double by the middle of the twenty-first century. In addition, scientists warn that Colorado’s climate has been heating up in recent decades and will most likely get even warmer. As temperatures rise, evaporation will increase and soil will dry out, reducing the amount of runoff in rivers while the thirst of cities and farms will increase. And snowpack will shrink and melt earlier in the spring, reducing the size of this critical reservoir and changing the timing of the water supply.

Limited supplies will force Coloradans to make difficult choices among the state’s municipal, agricultural, energy, recreation, and environmental needs. As of 2015, the widening gap between water supply and demand is being addressed in statewide collaborative efforts. Stakeholders with diverse interests are working together on a state plan that manages Colorado’s water supply to support the environment while maintaining vibrant cities, a robust agricultural sector, and productive industries. The state’s future depends to a large degree on the success of these efforts.