	Introduction

From its headwaters in Colorado and Wyoming to its terminus in the Gulf of California, the Colorado River Basin covers more than 246,000 square miles. The river runs through seven U.S. states (Wyoming, Colorado, Utah, New Mexico, Arizona, Nevada, and California) and Mexico. Pursuant to federal law, the Bureau of Reclamation (Reclamation, part of the Department of the Interior [DOI]) plays a prominent role in the management of the basin's waters. In the Lower Basin (i.e., Arizona, Nevada, and California), Reclamation also serves as water master on behalf of the Secretary of the Interior, a role that elevates the status of the federal government in basin water management. Colorado River water is used primarily for agricultural irrigation and municipal and industrial (M&I) purposes. The river's flow and stored water also are important for power production, fish and wildlife, and recreation, among other uses. Pursuant to the multiple compacts, federal laws, court decisions and decrees, contracts, and regulatory guidelines governing Colorado River operations (collectively known as the Law of the River ), Congress and the federal government play a prominent role in the management of the Colorado River. Specifically, Congress funds and oversees Reclamation's management of Colorado River Basin facilities, including facility operations and programs to protect and restore endangered species. Congress has also approved and continues to actively consider Indian water rights settlements involving Colorado River waters, and development of new and expanded water storage in the basin. In addition, Congress has approved funding to mitigate drought and stretch basin water supplies and has considered new authorities for Reclamation to combat drought and enter into agreements with states and Colorado River contractors. Under the compact, the states established a framework to apportion the water supplies between the Upper Basin and the Lower Basin, with the dividing line between the two basins at Lee Ferry, AZ, near the Utah border. The act ratified the 1922 compact, authorized the construction of a federal facility to impound water in the Lower Basin (Boulder Dam, later renamed Hoover Dam) and related facilities to deliver water in Southern California (e.g., the All-American Canal, which delivers Colorado River water to California's Imperial Valley), and apportioned the Lower Basin's 7.5 MAF per year among the three Lower Basin states. They express water storage conditions at Lake Mead and Lake Powell in terms of elevation, as feet above mean sea level (ft). For Lake Mead, the first level of shortage (1 st Tier Shortage Condition), under which Arizona and Nevada's allocations would be decreased, would be triggered if Lake Mead falls below 1,075 ft. For Lake Powell, releases under tiered operations are based on storage levels in both Lake Powell and Lake Mead (specific delivery curtailments based on lake levels similar to Lake Mead have not been adopted). However, Reclamation also projected that there was a 69% chance of a 1 st Tier Shortage Condition at Lake Mead beginning in January 2020. Improved hydrology for 2019 may decrease the likelihood of shortage in the immediate future. The results are expected to better inform managers how to provide water deliveries and conserve species. While natural flows have trended down, consumptive use in the basin has grown and has regularly exceeded natural flows since 2000. This imbalance between Lower Basin inflows and use, known as the structural deficit , causes additional stress on basin storage. After several years of negotiations, on March 19, 2019, Reclamation and the Colorado River Basin states finalized DCPs for both the Upper Basin and the Lower Basin. These plans required final authorization by Congress to be implemented. Following House and Senate hearings on the DCPs in early April, on April 16, 2019, Congress authorized the DCP agreements in the Colorado River Drought Contingency Plan Authorization Act ( P.L. 116-14 ). Upper Basin Drought Contingency Plan

The Upper Basin DCP aims to protect against Lake Powell reaching critically low elevations; it also authorizes storage of conserved water in the Upper Basin that could help establish the foundation for a water use reduction effort (i.e., a "Demand Management Program") that may be developed in the future. Similarly, Congress may be interested in the overall hydrologic status of the Colorado River Basin, as well as future efforts to plan for increased demand in the basin and stretch limited basin water supplies.
The Colorado River Basin covers more than 246,000 square miles in seven U.S. states (Wyoming, Colorado, Utah, New Mexico, Arizona, Nevada, and California) and Mexico. Pursuant to federal law, the Bureau of Reclamation (part of the Department of the Interior) manages much of the basin's water supplies. Colorado River water is used primarily for agricultural irrigation and municipal and industrial (M&I) uses, but it also is important for power production, fish and wildlife, and recreational uses.
In recent years, consumptive uses of Colorado River water have exceeded natural flows. This causes an imbalance in the basin's available supplies and competing demands. A drought in the basin dating to 2000 has raised the prospect of water delivery curtailments and decreased hydropower production, among other things. In the future, observers expect that increasing demand for supplies, coupled with the effects of climate change, will further increase the strain on the basin's limited water supplies.
River Management
The Law of the River is the commonly used shorthand for the multiple laws, court decisions, and other documents governing Colorado River operations. The foundational document of the Law of the River is the Colorado River Compact of 1922. Pursuant to the compact, the basin states established a framework to apportion the water supplies between the Upper and Lower Basins of the Colorado River, with the dividing line between the two basins at Lee Ferry, AZ (near the Utah border). The Upper and Lower Basins each were allocated 7.5 million acre-feet (MAF) annually under the Colorado River Compact; an additional 1.5 MAF in annual flows was made available to Mexico under a 1944 treaty. Future agreements and court decisions addressed numerous other issues (including intrastate allocations of flows), and subsequent federal legislation provided authority and funding for federal facilities that allowed users to develop their allocations. A Supreme Court ruling also confirmed that Congress designated the Secretary of the Interior as the water master for the Lower Basin, a role in which the federal government manages the delivery of all water below Hoover Dam.
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 an indicator of basin storage conditions. Under recent guidelines, dam releases from these facilities are tied to specific water storage levels. For Lake Mead, the first tier of "shortage," under which Arizona's and Nevada's allocations would be decreased, would be triggered if Lake Mead's January 1 elevation is expected to fall below 1,075 feet above mean sea level. As of early 2019, Reclamation projected that there was a 69% chance of a shortage condition at Lake Mead in 2020; there was also a lesser chance of Lake Powell reaching critically low levels. Improved hydrology in early 2019 may decrease the chances of shortage in the immediate future.
Drought Contingency Plans
Despite previous efforts to alleviate future shortages, the basin's hydrological outlook has generally worsened in recent years. After several years of negotiations, in early 2019 Reclamation and the basin states transmitted to Congress additional plans to alleviate stress on basin water supplies. These plans, known as the drought contingency plans (DCPs) for the Upper and Lower Basins, were authorized by Congress in April 2019 in the Colorado River Drought Contingency Plan Authorization Act (P.L. 116-14). The DCPs among other things obligate Lower Basin states to additional water supply cutbacks at specified storage levels (i.e., cutbacks beyond previous curtailment plans), commit Reclamation to additional water conservation efforts, and coordinate Upper Basin operations to protect Lake Powell storage levels and hydropower generation.
Congressional Role
Congress plays a multifaceted role in federal management of the Colorado River basin. Congress funds and oversees management of basin facilities, including operations and programs to protect and restore endangered species. It has also enacted and continues to consider Indian water rights settlements involving Colorado River waters and development of new water storage facilities in the basin. In addition, Congress has approved funding to mitigate water shortages and conserve basin water supplies and has enacted new authorities to combat drought and its effects on basin water users (i.e., the DCPs and other related efforts).