Laws the Shape the River

In 1922, following a decade of unusually high precipitation, the seven Basin States of the Colorado River drafted the Colorado River Compact. This agreement allocated 7.5 million acre-feet of water annually to the Upper Basin States and 7.5 million acre-feet annually to the Lower Basin States, as well as an additional 1 million acre-feet annually to the Lower Basin States to accommodate water in-flows that occur in the Lower Basin. . Subsequently, a U.S.-Mexico treaty allocated an additional 1.5 million acre-feet per year to Mexico (see Mexico Treaty section).
The Colorado River Compact holds the distinction of being the first interstate water compact in the United States.
A key provision of the Colorado River Compact is Article III(d), which stipulates that the Upper Division States shall not cause the flow of the Colorado River at Lee Ferry to fall below an aggregate of 75 million acre-feet for any ten consecutive-year period.

Therefore, any determination of whether the Upper Division States have failed to meet their non-depletion obligation to the Lower Basin would necessitate an inquiry into the factors causing the flows to drop below the 75 million acre-feet threshold over a ten-year period.

This international agreement guarantees Mexico an annual allocation of 1.5 million acre-feet of water from the Colorado River system.

The treaty includes provisions for reduced water allotments to Mexico during periods of extraordinary drought, although the specific criteria defining such conditions are not explicitly outlined within the document.

The International Boundary and Water Commission (IBWC) facilitates the implementation and management of this treaty. Subsequent “Minutes” issued by the IBWC clarify and provide further detail regarding the implementation of the treaty. These Minutes address specific operational aspects and interpretations, but do not alter the fundamental terms established in the original treaty.

The primary purpose of the 1948 Upper Colorado River Basin Compact was to apportion the Colorado River water allocated to the Upper Basin states under the 1922 Colorado River Compact.

The apportionment is defined as percentages of the total water supply available in a given year. The allocations of available supply are:

Colorado – 51.75%
New Mexico – 11.25%,
Utah – 23%
Wyoming – 14%.

For example, under a full supply of 7.5 million acre-feet for the Upper Basin, Colorado’s share would be approximately 3.8 million acre-feet. If the available supply is reduced to 6 million acre-feet, Colorado’s share would be approximately 3.1 million acre-feet, with the other States’ allocations adjusted proportionally.

The Upper Colorado River Commission (UCRC) is an interstate administrative agency established by the 1948 Upper Basin Compact. This agency is unique because the obligations outlined in both the Colorado River Compact and the Upper Basin Compact are shared among these Upper Division States, rather than a direct delivery obligation to a specific state line.

The UCRC undertakes various activities to facilitate the administration of the interstate compact, including:

Establishing rules and regulations for compact implementation
Forecasting water runoff in the Colorado River and its tributaries
Conducting cooperative studies of the Colorado River System’s water supplies
Collecting and reporting data on streamflows, storage, diversions, and water use within the tributaries of the Upper Basin
Making findings regarding flows at Lee Ferry
Making findings regarding the necessity and extent of curtailment, if required

It is important to note that the UCRC does not control the in-state administration of water rights, which remains the responsibility of the individual States.

The “Big Three” Today

These three foundational documents, along with subsequent laws, agreements, and judicial decrees, collectively form what is known as the Law of the River (LoR). This body of legal instruments seeks to balance the need for certainty in water resource planning with the flexibility required to adapt to evolving conditions within the Colorado River Basin.

Opportunities continue to exist within the current legal framework to find flexible solutions for addressing contemporary challenges, such as climate change and increasing water demands, for present and future generations.

Beyond the “Big Three” compacts and treaty, several federal laws and a significant equitable apportionment decree have played a crucial role in shaping the management of the Colorado River. These include:

The 1928 Boulder Canyon Project Act
This act ratified the Colorado River Compact and authorized the construction of Hoover Dam, creating Lake Mead.

The 1963 U.S. Supreme Court Decision in Arizona v. California
This landmark decision apportioned the waters of the Lower Basin among the states of Arizona, California, and Nevada. The Court also affirmed that all waters in the Lower Basin are under the control of the United States and settled federal reserved water rights to the mainstream of the Lower Colorado River for five Tribal Nations.

The 1956 Colorado River Storage Project Act
This legislation authorized the development of major water storage facilities in the Upper Basin, including the construction of the Glen Canyon Dam (forming Lake Powell), Flaming Gorge Dam, Navajo Dam, and the Aspinall Unit dams. It also facilitated numerous participating projects, many of which are located in Colorado.

The 1968 Colorado River Basin Project Act
This act authorized the Central Arizona Project and established the order of priority for water releases from Lake Powell to meet authorized purposes. It also authorized storage in Lake Powell, often referred to as 602(a) storage, to help the Upper Division States manage through critical drought periods without the need to curtail existing water rights in the Upper Basin.