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Coloradans might know of Lake Powell from sun-filled days recreating in its waters, its expansive, rust-colored canyon walls … or the onslaught of news coverage focused on its water levels.

So why is the lake — and the white ring discoloring the rock walls above it — important to the Colorado River?

This 10-question guide breaks down the role of Lake Powell in the Colorado River Basin, which is experiencing one of its worst droughts in 1,200 years. As one of the continent’s largest artificial lakes, Powell plays a role in water storage and release, local economies, environmental debates and regional electricity production. After its stored water dropped to historic lows in recent years, state and federal officials began negotiating how the reservoir’s operations should change during water shortages in the future.

“As a result of Lake Powell hitting critical levels our reservoirs were called on to provide protection for Powell,” said Amy Ostdiek with the Colorado Water Conservation Board, the state’s top water agency. “That highlights how Lake Powell impacts us in Colorado, and also how what happens at Lake Powell is a direct result of what happens at Lake Mead — therefore it’s all tied to Lower Basin overuse.”

Colorado River Explained. We’re answering your questions about the Colorado River. Send them our way and stay tuned for more!

What is Lake Powell?

Lake Powell is one of two massive water storage reservoirs for the Colorado River Basin, which provides water for 40 million people in the West. The reservoir was formed by Glen Canyon Dam in northern Arizona, and its waters extend northeast into southern Utah. 

The reservoir collects water from Colorado, New Mexico, Utah, Wyoming, part of Arizona and tribal reservations in the Colorado River’s Upper Basin. The Upper Basin dam releases water downstream to Lower Basin states — Arizona, California and Nevada — more than 20 Native American tribes and Mexico.

Glen Canyon Powerplant also generates hydroelectricity, and the Glen Canyon National Recreation Area attracts about 3 million people annually, which helps bolster local economies. 

Lake Powell and a downstream reservoir, Lake Mead, can store up to 53.9 million acre-feet of water, or about 92% of the reservoir storage capacity in the entire Colorado River Basin. The basin’s total capacity is 58.48 million acre-feet. 

One acre-foot supports two families of four to five people for one year.

The reservoir is named after John Wesley Powell, who successfully navigated the first expedition down the Colorado River through the Grand Canyon in 1869.

A dam in the middle of a body of water.
Lake Powell, which is impounded by Glen Canyon Dam, was partially filled July 13, 2023. The dam is near Page, Arizona, about 5 miles south of the Arizona-Utah border. (U.S. Bureau of Reclamation)

How is Lake Powell connected to Colorado?

Lake Powell and Colorado are connected by the Colorado River, which begins in Rocky Mountain National Park near Kremmling. Colorado River water reaches every corner of the state. In fact, Coloradans rely on its water for drinking, municipal, agricultural, industrial, recreational and environmental purposes. Hydropower production revenues from Glen Canyon Dam help fund Endangered Species Act programs in Colorado.

Colorado and other Upper Basin states are also tied to the Colorado River by a 1922 interstate compact, court decisions and decrees, federal laws, regulations and other legal agreements established over the last century. Collectively, this “Law of the River” establishes how the Colorado River’s water is shared.

In emergency situations, like those seen in 2021 and 2022, certain Colorado dams may be required to send additional water to Lake Powell. These upstream dams include Crystal Dam, Blue Mesa Dam and Marrow Point Dam, which form the Aspinall Unit located along the Gunnison River in Colorado. 

These dams are part of the federally operated Colorado River Storage Project authorized in 1956, which also includes Flaming Gorge Dam in Utah and Navajo Dam in New Mexico.

What is Lake Mead?

Lake Mead is the largest reservoir in the Colorado River Basin and the United States. 

The federal government built and operates Lake Mead, which sits in the river’s Lower Basin. In 1936, the Bureau of Reclamation constructed Hoover Dam near Las Vegas, forming the massive reservoir that runs along the Nevada-Arizona border.

Lake Mead’s purpose is to store and release water for municipal, industrial, power generation and agricultural purposes. Some of its storage capacity is also designated for flood and sedimentation control. The reservoir’s water goes to downstream users in Arizona, California, Nevada, tribal reservations and Mexico. 

Lake Mead was the first national recreation area in the U.S., and it attracts more than 9 million visitors each year. It was named after Elwood Mead, the Bureau of Reclamation commissioner when the reservoir was formed.

A view of the Hoover Dam in Nevada with white lines along the rocks.
Lake Mead, which is impounded by Hoover Dam, was partially full July 28. The dam is located less than 40 miles southeast of Las Vegas. (Connie Castle, U.S. Bureau of Reclamation)

Why are there white rings around Lake Powell and Lake Mead?

Sometimes referred to as the “bathtub ring,” the white ring is caused by the calcium carbonate and other hard minerals in the water that attach to the sandstone walls of the reservoirs.

The top of the ring indicates the high-water mark. Visitors can see such a large ring because the water levels in Lake Powell and Lake Mead have declined over the past two decades, reaching historic lows in the early 2020s.

Experts attribute this decline to prolonged drought, a changing climate and overuse by water users in the basin.

Current water levels

What does full pool mean?

A reservoir’s full pool is its total capacity. When Lake Powell’s water level is about 3,700 feet above sea level, the reservoir can hold about 26 million acre-feet of water. In fact, the reservoir filled for 17 years before first reaching its full capacity in 1980.

Lake Powell’s “live” storage capacity is 23.3 million acre-feet of water, according to the Bureau of Reclamation. Why is that different? Some of the reservoir’s water is too low to be released by Glen Canyon Dam.

What is dead pool?

Dead pool occurs when the amount of water stored in a reservoir is so low that it can no longer flow downstream.

Lake Powell reaches dead pool when it falls below 3,370 feet in elevation, which equals about 1.7 million acre-feet of water behind the dam. At this point, water managers cannot send stored water through Glen Canyon Dam to Lake Mead and millions of downstream water users. 

Temporary and permanent dead pool conditions would unleash widespread impacts on communities and the environment.

The Bureau of Reclamation released water from Lake Powell through Glen Canyon Dam in late April 2023 as part of a high-flow experiment. The springtime pulse of water was meant to move and redeposit sand and sediment, which helps rebuild beaches and provide habitat for wildlife in the Grand Canyon. (Bureau of Reclamation)

What does minimum power pool mean?

The minimum power pool is the lowest water elevation at which water can flow through the intake valves in a dam to generate hydroelectric power. At Lake Powell, the water level needs to be above 3,490 feet or about 3.7 million acre-feet of water that can be delivered downstream.

Glen Canyon Powerplant produces about 5 billion kilowatt-hours of hydroelectric power annually. The power is distributed to Colorado, Wyoming, Utah, New Mexico, Arizona, Nevada and Nebraska.

If Lake Powell falls below 3,490 feet, it cannot generate hydroelectric power, which would impact people across the West. When the reservoir reaches its buffer elevation of 3,525 feet, it triggers a series of actions to try to stop the lake from reaching its minimum power pool elevation.

What are Lake Mead’s key water levels?

At full capacity, Lake Mead’s water elevation is 1,229 feet above sea level and it stores 28.9 million acre-feet of water. That’s enough to cover Pennsylvania in one foot of water. 

At 950 feet, the reservoir hits its minimum power pool and can no longer generate hydroelectric power. At this elevation, it stores 4.55 million acre-feet of water. At 895 feet, it hits its dead pool. About 2.55 million acre-feet of water is still in the reservoir, but its elevation is too low to pass through the dam’s intake valves.

Why do Lake Powell’s water levels change?

Lake Powell’s water levels change as a result of environmental factors and how the reservoir is managed. 

The Colorado River’s water supply naturally fluctuates from year to year based on the amount of precipitation, evaporation, the loss of water to leaky infrastructure and dry soils that suck up water. Prolonged drought, increasing temperatures and a changing climate have thrown off this natural fluctuation and decreased the river’s water supply, experts say. 

Lake Powell’s water levels are also impacted by its operations — how it stores water and releases it to Lake Mead — which were established in a 2007 agreement between states and the federal government. Under these guidelines, the reservoirs’ levels must be balanced, which means sometimes extra water stored in Lake Powell is released to Lake Mead. 

In general, reservoirs can act like water savings banks by keeping extra water in wetter-than-average years. These savings help insulate downstream water users from water shortages in drier years. Colorado’s top water agency says the Lower Basin’s reliance on Lake Mead and Lake Powell as savings banks has perpetuated overuse — and helped deplete both reservoirs.

All basin states and tribes are negotiating ways to adapt their water use to the river’s changing conditions as concerns about water insecurity increase.

Are Lake Mead and Lake Powell running out of water?

No. Well, not yet. The two enormous reservoirs are balancing between crisis and relative stability, and future hydrological conditions could swing the reservoirs in either direction.

As of summer 2023, there was enough water in both reservoirs to generate hydroelectric power and deliver water to downstream users through Hoover Dam and Glen Canyon Dam. 

But the Colorado River Basin’s total system storage was still low. The system held less than 44% of its total capacity, 58.48 million acre-feet, as of July. This is after the above-average snowpack and spring precipitation in the Colorado River Basin helped Lake Mead and Lake Powell recover slightly from historic lows. 

Lake Powell and Lake Mead took many years to fill in the first place — they can’t recover in one year, experts say. It would take 10 years of average inflows, about 9.6 million acre-feet, and releases, about 8.23 million acre-feet, to fill Lake Powell, according to the Bureau of Reclamation.

Even with an above-average water year, the two reservoirs could quickly return to near-crisis conditions like those in June 2022, when the river’s system of reservoirs was at 35% total capacity. 

Some projections show that Powell would stop producing electricity before 2026 if its average inflows between 2023 and 2026 fall below 79% of the 30-year average, and if officials take no action to protect the reservoir, according to a 2022 federal analysis.The Bureau of Reclamation announces its water operation plans for the upcoming calendar year in an August report, known as the 24-month study. Those plans can be updated in April.


Shannon Mullane writes about Western water issues for The Colorado Sun and her work is funded by a grant from the Catena Foundation. She focuses on the Colorado River Basin, tribal affairs related to water, and West Slope water issues.
Born in East Tennessee, Shannon has been in Colorado for a decade or so and is holding down the fort in Durango, the Sun's latest outpost. Before joining the Sun's team, she contributed award-winning reporting on government, environment, health and more as a staff writer for The Durango Herald and as an intern for the Colorado Independent. She also earned a master's in journalism from the University of Colorado Boulder. Shannon is conversational in French, trying really hard in Spanish, and often spotted baking or enjoying live music.