The Hardest-Working River in the West

Managing water supply and demand among states, countries, and 30 sovereign Native American tribes requires navigating a myriad of agreements and treaties, judicial rulings, statutes, regulations, and contracts that are collectively referred to as the “Law of the River.” Decisions are complicated when cities look to meet their growing populations’ numerous water demands with water that is already being used to grow fruits and vegetables and support meat and dairy operations. Another source of complexity involves keeping water in the river for recreation and to conserve and protect wildlands and wildlife.

National, state, tribal, and local water managers and land use planners try to balance honoring historical water rights, allocating water for new economic uses, and preserving a healthy, thriving, and resilient environment for future generations.  

Surface water in the Basin states is governed by the legal doctrine of prior appropriation, which means that older water rights take precedence over newer ones.

Although Native Americans have used and managed the Colorado River Basin’s water for centuries, only within the last century were they required by the U.S. legal system to have rights to use those waters (see “1908” in timeline below). Many are still working to realize their rights and obtain their rightful allocations. 

The first interstate agreement, the  Colorado River Compact   (signed by six of the seven U.S. Basin states in 1922 and ratified by the U.S. Congress in 1928), divided the Basin into Upper and Lower basins. The Compact is widely thought of as the cornerstone or foundation of the Law of the River. 

The Law of the River governs water allocations among the seven U.S. Basin states (Arizona, California, Colorado, Nevada, New Mexico, Utah, Wyoming), including areas within those states that use water diverted and exported from the river. The law also governs volumes and salinity standards for deliveries to Mexico, operations during shortage and surplus conditions, and the water entitlements of 30 Native American tribes. 

In 1908, the U.S. Supreme Court  decided  that when the U.S. government designates or “reserves” land for federal purposes, including for Indian reservations, that land comes with water rights. This special federal status and the early establishment dates for reservations' tribal water rights gives them a higher priority than other water rights. However, the specific volume of water each tribe has a right to use must be determined through lengthy and complicated legal proceedings. Tribes have had to endure multiple water equity and access challenges and invest considerable time, effort, and money fighting to have their rights quantified.

Twenty-two of the 30 Basin tribes have recognized rights to about one-fifth of the water in the Basin ( Water & Tribes Initiative, 2021 ). However, not all of these tribes are able to use the water they have rights to for reasons that include insufficient infrastructure and funding, aging and inefficient delivery systems, and constraints on off-reservation use. Additionally, 12 tribes have water rights claims that are partially or totally unresolved, a source of uncertainty for both tribal and nontribal water users. 

The map below contains information about the water entitlements of all 30 federally recognized tribes in the Colorado River Basin, synthesized from various published sources.

See these sources to explore tribal water rights further:

When the river was divided up by the 1922 Compact, the Basin was experiencing an unusually wet period, after major drought in the late 1800s. In light of that high variability, it made sense to base water allocations on the long-term-average flow of the river. Some experts at the time estimated it was 15 MAFY or less, but the Compact architects based their allocations on a more optimistic estimate of 17.5 MAFY ( Kuhn and Fleck, 2019 ). 

Today, the Commissioner of the U.S. Bureau of Reclamation (USBR)—the designated “watermaster” of the Lower Basin—decides how much of their full allocation Lower Basin water users will receive based on anticipated water levels for Lake Powell and Lake Mead in the coming year. USBR’s updated projections of future hydrologic conditions and corresponding reservoir operations are described in monthly  24-Month Study reports . August reports have special importance because they establish whether an official shortage in the Lower Basin will be declared for the following year.  

In August 2022, 100 years after the Colorado River Compact was signed, the USBR Commissioner declared a “Tier 2a” shortage for 2023, meaning those with lower-priority water rights on the river (water users in Central Arizona and Nevada) must take even greater cuts to their water deliveries than they did the previous year. The Secretary of the Interior also called on all Basin states to identify two to four MAFY of additional reductions to stabilize the river. Drought tiers and shortage sharing arrangements are discussed in the next chapter, Of Storage and Shortages.

Ninety percent of the surface water in the Colorado River comes from Rocky Mountain snowmelt in the spring and reaches the main stem of the river through networks of smaller tributary streams ( Jacobs, 2011 ). Significantly, about half the streamflow in the Upper Basin comes from baseflow derived from groundwater discharged into streams and tributaries connected to the Colorado River ( Rumsey et al., 2015 ). Most of that baseflow is sourced from high-elevation areas that receive most of their precipitation in the form of snow. Pumping groundwater for any use diminishes streamflows where groundwater and surface water are connected. 

The upstream flows in the Basin are captured, stored, and distributed to fulfill water rights obligations via an expansive system of dams and diversions. 

Although many nonfederal dams exist in the Basin, most of the large-scale storage and distribution systems for the Colorado River’s main stem and major tributaries are federal projects constructed between the 1930s and 1970s. Federal reservoirs also serve other purposes such as hydropower generation, flood control, and recreation. 

“The water level’s elevation above sea level is a proxy for the amount of water in the reservoir. Lake Mead is full when the water level is at roughly 1,220 feet above sea level.”—Matt Jenkins

Signed into effect on April 16, 2019, the Colorado River Drought Contingency Plan Authorization Act authorizes a set of agreements, Drought Contingency Plans (DCPs), among the seven Colorado River Basin states and the U.S. Department of the Interior that provide additional security and certainty in the water supply of the Colorado River system to benefit the people it serves. The agreements include the Upper Basin Drought Contingency Plan (Upper Basin DCP) and Lower Basin Drought Contingency Plan (Lower Basin DCP). 

In addition to the U.S. DCPs, Mexico also agreed to participate in measures to protect and conserve the Colorado River water supply through Minute 323 (2017), the  Binational Water Scarcity Contingency Plan , as long as the U.S. adopted both Lower Basin and Upper Basin DCPs.  

 Minute 319  and  Minute 323  of the United States–Mexico Water Treaty outline how the water allocation to Mexico will be affected by the elevation levels of Lake Mead. While this international agreement was signed in September 2017, water scarcity reductions were put into effect only after the U.S. DCPs were signed in 2019. (other components of Minute 319 took effect when Minute 323 was signed.) 

While significant progress has recently been made, the current DCPs and guidelines are effective only until 2026. Discussions about post-2026 policies have been heightened by the U.S. Bureau of Reclamation’s August 2022 declaration that the states must find two to four MAF of additional water to conserve beyond the existing DCP requirements. 

In this section, we highlight two of the overarching challenges to water management and sustainability in the Basin. Current and future water supplies and water demands will shape the economy and environment of the Basin. 

The first major hurdle for water management within the Colorado River Basin is the uncertain water supply. While the river’s water supply is already complicated and constrained by issues associated with the Law of the River, a more contemporary threat is the increasing variability of climate, extreme weather events, and the rising hazards of climate change. 

Rocky Mountain snowpack is another important variable for water supply. The National Oceanic and Atmospheric Administration reports daily on  snow water equivalent (SWE), the liquid water equivalent of the snowpack expressed in terms of depth . The Natural Resources Conservation Service, together with the National Water and Climate Center, tracks SWE through their  SNOTEL network  throughout the Rocky Mountains.

Check out the article "Beyond Drought" from the January 2019 issue of Land Lines which discusses recent droughts, the Drought Contingency Plan, and what can be done about water shortages: 

Another source of uncertainty is the water supply and demand implications of rapid urbanization in the Basin. Many of the nation’s fastest-growing regions and communities are in the Colorado River Basin or in adjacent areas that use Colorado River water. 

In central Arizona, for example, much of the urbanization in the Phoenix metro area has occurred on previously irrigated farmland. Replacing farms with less thirsty urban landscapes contributed to a decrease in overall regional water use in Maricopa County. However, as most of the agricultural lands surrounding metro Phoenix became urbanized,  total water demand stopped decreasing and leveled off . This change also resulted in “hardened” demand, meaning that during drought, temporarily reducing demand for urban uses is more difficult than for agricultural ones. Without a reserve of farmland to convert, pressure for more development and density may lead to increasing regional water use. For fast-growing urban areas in the Basin, the key challenge is accommodating more residents with less water. 

While communities throughout the Southwest have experienced significant growth, many have done a great deal more with less water. After per capita water use rates rose through the 1980s and into the 1990s, these trends have now shifted. By substantially increasing water efficiencies, cities have been able to bring down per capita water consumption while adding many more people. Although in many cases more water savings from conservation is still possible, key questions for cities are, What is the limit for efficiency, Are there new innovations, and What happens after the limit is reached? 

Water managers and land use planners throughout the Colorado River Basin are working with elected and appointed officials, scientists, foundations, NGOs, and their local businesses, developers and residents to address our current and future challenges. In this section, we highlight partnerships and initiatives involving tribal communities before sharing activities in which the Babbitt Center takes part, to address potential water shortages by integrating land and water management. First, we present a 20-year timeline of historic and innovative policies and programs that have ushered us into a new era of management and conservation.  

To learn more about land and water in the Colorado River Basin, check out these sites: 

•  Colorado River Science Wiki : A web-based clearinghouse for scientific and technical information relevant to the Colorado River Basin and the management of its water resources and related natural resources. 
• Western Water Assessment’s  Colorado River Basin Climate and Hydrology: State of the Science : A report that aims to create a shared understanding of the physical setting and the latest data, tools, and research underpinning the management of Colorado River water resources. 
•  Central Arizona Project (CAP) Canal System StoryMap : This highlights key features of the CAP system, an engineering marvel and key infrastructure of the Colorado River system. 
• The Kyl Center for Water Policy at Morrison Institute’s  “Colorado River Shortage” StoryMap : Explores the implications of the Colorado River shortage for Arizona and the  Arizona Water Blueprint : A set of interactive, data-rich maps of Arizona’s water resources and infrastructure. 
• The Lincoln Institute of Land Policy’s  “Making Sense of Place | Phoenix” : One of America’s largest and fastest-growing cities, Phoenix has attracted newcomers for decades with its warm weather and plentiful land. But in the face of a hotter, drier future, the sprawling desert metropolis is working to chart a more sustainable course. 

About the Lincoln Institute of Land Policy and the Babbitt Center for Land and Water Policy

Colorado River Basin GIS Open Data Portal

The Babbitt Center has created a data portal that contains the maps, tables, and related reports seen or mentioned in this StoryMap as a way for readers to download and explore the data themselves. Click below to access this GIS open data portal: