Mainstem Lower Colorado River Basin Arizona

1. Basin Overview
The Navajo Nation has water rights claims in the Mainstem Lower Colorado River located in the Lower Colorado River Basin. The Basin includes the northern portion of Bodaway-Gap Navajo Chapter in North-Central Arizona.

Under The Colorado River Compact of 1922, the seven basin states established a framework to apportion the water supplies between the Upper Basin and the Lower Basin; each were apportioned 7.5 million acre-feet (MAF) annually for beneficial use. The dividing line between the two basins is at Lees Ferry, AZ. 

In 1928, Congress approved the Boulder Canyon Act that divided the 7.5 MAF among three Lower Basin states giving 4.4 MAF to California, 2.8 MAF to Arizona, and 300,000 acre-feet to Nevada per year. The 2.8 MAF to Arizona includes Tribal water rights.

2. Hydrology

Most of the Lower Colorado River Basin’s water flow is determined by the amount released from Glen Canyon Dam, a project authorized by Congress in 1956 to provide water storage in the Upper Basin. The U.S. Bureau of Reclamation and basin stakeholders closely track the status of two large reservoirs—Lake Powell in the Upper Basin and Lake Mead in the Lower Basin—as indicators of basin storage conditions that determine releases from both lakes. Since the onset of drought in the early 2000s,storage levels at these reservoirs have been falling.

It is important to note that the Colorado River Compact was based on an average annual flow of 16.4 MAF per year. However, from 1906 to 2022, the observed flow at Lees Ferry averaged 14.6 MAF annually. Natural flows from 2000 to 2022 (i.e., during the ongoing drought) averaged less than 12.1 MAF annually, with this period noted to be the driest 23-year period on record.[1] At the same time, consumptive use and losses (e.g., evaporation) in the basin have regularly exceeded natural flows, especially during the current drought, which is estimated to be the driest period the region has seen in over 1,200 years. Recent studies have concluded that Colorado River flows are unlikely to return to 20th century averages and that future water supply risk is high.[2] Overall, natural flows have declined by approximately 20% over the last century. One study attributed more than half of this decline to climate change. Although there is potential for some precipitation increases in the region due to climate change, such potential increases are not expected to counteract this condition. The region is projected to become drier still.[3] The Department of the Interior is initiating the formal process of developing future operating guidelines and strategies to protect the stability and sustainability of the Colorado River. The new guidelines will replace the 2007 Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead, which expire at the end of 2026.

3. History Regarding Water Rights

There have been two settlement attempts to apportion the Navajo Nation’s water rights for the Mainstem of the Lower Basin. The first, in 2010, proposed a Mainstem quantity of 31,000 acre-feet per year. In 2012, the Arizona Department of Water Resources reserved Mainstem water for future settlements, including 22,589 AFY of the CAP NIA priority water referred to in section 1 04(a)(1)(A)(iii) of the Arizona Water Settlement Act for use in a future settlement of the claims of the Navajo Nation to Lower Colorado River water. According to the Act, the Secretary shall retain the 3,500 AFY of un-contracted Arizona fourth priority, 2,000 AFY shall be retained for use in a future settlement of the claims of the Navajo Nation to Lower Colorado River water. Additionally, an amount of 6,411 AFY of CAP Water shall be available for diversion and use from the San Juan River pursuant to and consistent with section 10603(b)(2)(D) of the Northwestern New Mexico Rural Water Projects Act.

In 2023 the United States Supreme Court heard and gave an opinion in Arizona v. Navajo Nation. In the case’s majority opinion, the Nation’s water rights were affirmed, thereby Nation’s water rights were not lost.


 4. Current Status: Litigation, Settlements, Etc.
The Navajo Navajo is currently engaged in settlement negotiations for water rights in Arizona that include the Mainstem of the Lower Basin.


Congressional Research Service (July, 2021). Management of the CR: Water Allocations Drought and the Federal Role

Terms Of UsePrivacy StatementCopyright 2024 by NNDIT
Back To Top