Colorado River Timeline

Timeline of Colorado River Compact & Key Events

The Colorado River is often described as the most regulated river in the world with a complex and extensive history surrounding its development. Balancing river resources among states and other interests is an ever-evolving process. In addition to the 1922 Colorado Compact, there have been subsequent agreements, federal laws, and court decisions that define how the river is managed. These are commonly referred to as “The Law of the River” and are highlighted along with key historical events on the timeline below.

  • Summer 1869

    Colorado River & Grand Canyon Exploration

    Colorado River & Grand Canyon Exploration

    Major John Wesley Powell, a Civil War veteran, led a team of nine men in four small wooden boats on an exploration of the Colorado River and Grand Canyon. There are no photos from his first trip but some like this one exist from his second expedition in 1871. Photo credit National Park Service
  • 1889

    International Boundary and Water Commission Created

    The International Boundary and Water Commission was created by the U.S. and Mexico and is responsible for applying the boundary and water treaties between the U.S. and Mexico and settling any differences that may arise as a result of their application.
  • Nov. 24, 1922

    1922 Colorado River Compact Signed

    1922 Colorado River Compact Signed

    Negotiated by the seven basin states and the federal government, the 1922 Colorado River Compact defines the relationship between the Upper Basin states (Colorado, New Mexico, Utah and Wyoming) and the Lower Basin states (Arizona, California and Nevada). Recognizing the need each individual state would have to develop water at different times, the compact protects each state’s right to develop its allocation on its own time frame. Each basin has the right to develop and use 7.5 million acre-feet of river water annually. Photo credit Bureau of Reclamation
  • 1928

    Boulder Canyon Project Act

    Boulder Canyon Project Act

    Boulder Canyon Project Act ratified the 1922 Compact and authorized the construction of the Hoover Dam and lower basin irrigation facilities. California was apportioned 4.4 million acre-feet of water per year; Arizona 2.8 million acre-feet; Nevada 300,000 acre-feet. The dam was officially dedicated Sept. 30, 1935, and later renamed Hoover Dam in 1947 after President Herbert Hoover. Photo credit Ansel Adams, Our Documents
  • 1935

    Lake Mead

    Lake Mead

    Lake Mead, a man-made reservoir 25 miles southeast of Las Vegas, was created by the completion of Hoover Dam in 1935. It is the largest reservoir in the U.S.
  • Feb. 3, 1944

    Mexican Treaty

    Mexican Treaty

    Treaty for the Utilization of Waters of the Colorado and Tijuana Rivers and of the Rio Grande (commonly called the “Mexican Treaty”) committed 1.5 million acre-feet of Colorado River water per year to Mexico. Photo credit International Boundary and Water Commission
  • 1948

    Upper Colorado River Basin Compact

    The Upper Colorado River Basin Compact created the Upper Colorado River Commission and outlined its roles and responsibilities. This compact also apportioned the Upper Basin’s 7.5 million acre-feet among Colorado (51.75%), New Mexico (11.25%), Utah (23%) and Wyoming (14%). The portion of Arizona that lies within the Upper Colorado River Basin was apportioned 50,000 acre-feet annually. 
  • 1956

    Colorado River Storage Project Act

    Colorado River Storage Project Act authorizes the construction of Glen Canyon, Flaming Gorge, Navajo and Curcanti dams. The Act also authorized the construction of several other projects throughout the Upper Colorado River Basin, including the Central Utah Project and Emery County Project.
  • 1963

    Arizona v. California Supreme Court Decision

    The Arizona v. California Supreme Court case settled a dispute filed in 1952 over claims to Colorado River waters in the river’s Lower Basin. The court specified the amount of water to which each basin state was entitled. These amounts were adjusted in a 1964 decree. Nevada, New Mexico, Utah, and the United States were subsequently added as parties to the proceedings. The controversy centered on how much water each state had a legal right to use from the Colorado River and its tributaries.
  • Sept. 13, 1963

    Lake Powell

    Lake Powell

    When Glen Canyon Dam was completed on Sept. 13, 1963, Lake Powell began to fill. It took 16 years to fill to the 3,700 feet level on June 22, 1980. It was built to store water for Utah, Colorado, New Mexico and Wyoming and help the Upper Basin meet their obligation to the Lower Basin states, while not impairing the ability of the Upper Basin to fully develop their allocation. This water is also used for recreation, power generation and delivering water to Arizona, California and Nevada.
  • Sept. 30, 1968

    Colorado River Basin Project Act

    The Colorado River Basin Project Act authorized the Secretary of the Interior to construct a variety of dams, power plants, reservoirs and related works. The Act also authorized and directed the Secretary, in connection with the development of the Colorado River Storage Project and participating projects, to investigate, plan, construct and operate facilities to mitigate losses of, and improve conditions for, fish and wildlife and public recreational facilities. The Act provided authority to acquire lands and to lease or convey lands and facilities to State and other agencies.
  • 1970

    Long-Range Operating Criteria

    Section 602 of the Colorado River Basin Project Act is called the Long-Range Operating Criteria. These criteria are designed to control the coordination of the long-range operation of the storage reservoirs in the Colorado River Basin as part of the Colorado River Storage Project Act and the Boulder Canyon Project Act, which constructed Lake Mead. The Secretary of the Interior initiates a formal review of the Operating Criteria at least every five years.
  • 1973

    Minute 242

    Minute 242 of the U.S.-Mexico International Boundary and Water Commission set a salinity standard that helped reduce the salinity of water the U.S. delivered to Mexico at Morelos Dam in Baja, California.
  • 1974

    Colorado River Basin Salinity Control Act

    Colorado River Basin Salinity Control Act authorized desalting and salinity control projects including the Yuma Desalting Plant.
  • 2001

    Colorado River Interim Surplus Guidelines

    Guidlines that facilitated California’s reduction in demands on the Colorado River to 4.4 million acre-feet per year by the year 2015.
  • 2007

    Interim Guidelines

    The 2007 Interim Guidelines are currently in place to manage the river’s reservoirs and allocate shortages and were put in place after enduring the worst seven-year drought on record. They determine when and how much water is released from Lake Powell. They also outline the cuts Arizona and Nevada take as water levels drop in Lake Mead. The guidelines expire in 2026 and negotiations begin in 2021. The Bureau of Reclamation is currently conducting a formal review to evaluate the effectiveness of the guidelines.
  • Nov. 20, 2012

    Minute 319

    Minute 319 of the U.S.-Mexico International Boundary and Water Commission signing in Coronado, California provided water for environmental flows for the Colorado River Delta.
  • Sept. 21, 2017

    Minute 323

    Minute 323 states that Mexico can continue to store water in Lake Mead; lays out how the two countries will make voluntary cutbacks in times of drought; commits the U.S. to financially supporting water efficiency projects in Mexico that will save more than 200,000 acre-feet of water in return for a one-time water exchange; and requires both countries to provide water and funding for habitat restoration and scientific work in the Colorado River Delta for 10 years.
  • May 20, 2019

    Drought Contingency Plan Signing

    Water officials from all seven Colorado River Basin states joined representatives from the Department of the Interior and Bureau of Reclamation May 20, 2019, to sign drought contingency plans for the Upper and Lower Colorado River basins. These plans are designed to reduce risks from ongoing drought and protect the Colorado River. The Upper and Lower Colorado River basin states have developed contingency plans both independently and collaboratively. The product of these discussions is five documents that comprise the Drought Contingency Plan for the Colorado River. Photo credit Bureau of Reclamation

    They include:

  • 2021

    Interim Guideline Renegotiations Begin

    Seven basin states begin Interim Guideline renegotiations to address reservoir management based on the latest hydrology and climate data.
  • 2026

    Interim Guidelines finalized and adopted.