The Colorado River system in charts

The Colorado River supplies about 40 million people across seven states and Mexico (what states the Colorado River flows through maps the route and each state's share), and almost all of its stored water sits in two reservoirs: Lake Powell behind Glen Canyon Dam, and Lake Mead behind Hoover Dam. Powell is the upper basin's bank, Mead is the lower basin's, and between them they hold the large majority of the system's storage. Watch those two lines and you are watching the river.

The 1922 split, and the math problem inside it

The 1922 Colorado River Compact divided the river between an upper basin and a lower basin, 7.5 million acre-feet each per year, with 1.5 million acre-feet later guaranteed to Mexico by treaty. Add those up and the paper allocation comes to 16.5 million acre-feet. The trouble is that the river has often produced less than that, and less still in the dry decades since 2000. The system was promised more water than it reliably yields, and Powell and Mead have absorbed the difference by drawing down.

The two banks, live

The charts above are Powell then Mead, current storage against their normal-for-the-date bands. The two move together because they are one plumbing system: Glen Canyon releases from Powell flow downstream to refill Mead. When people talk about the Colorado River crisis, this pair of lines is the crisis, measured.

Lake Mead's own record runs back to 1935: Lake Mead water level by year has the level at the end of every year, from the first fill behind Hoover Dam through the 1983 high to the lows of 2022 and 2026.

The elevations that make headlines

The alarms on the Colorado are written in feet of surface elevation. At Lake Powell, minimum power pool is elevation 3,490 feet, the level below which Glen Canyon Dam can no longer generate hydropower, per Reclamation. Below that, water can leave only through the river outlet works, and dead pool, near elevation 3,370 feet, is where even gravity releases become uncertain. At Lake Mead, Reclamation puts dead pool at elevation 895 feet, with the Hoover Dam power pool historically at 1,050 feet, now extended lower with wide-head turbines. The charts above track storage in acre-feet; each reservoir's page also carries its daily surface elevation in feet, the unit these thresholds are written in. What is dead pool at Lake Mead and Lake Powell? lays out every threshold, with each lake's distance from the power and dead pool lines on its latest reading.

A system in renegotiation

The 2007 Interim Guidelines that tied Glen Canyon Dam's releases and Lake Mead's shortage tiers to the two lakes' elevations governed operations through 2026. Reclamation's Sep 15, 2026 24-Month Study runs operating year 2027 under new 2027-2028 Operating Guidelines, issued under a 2026 Record of Decision covering 2027 through 2036, with Lake Powell in a Low Elevation Infrastructure Protection Range and a shortage condition governing Lake Mead in 2027. The Waterline reports that framework and the storage as Reclamation publishes them.