The Colorado River after 2026

Lake Powell, behind Glen Canyon Dam, and Lake Mead, behind Hoover Dam, store the Colorado River's water for seven US states and Mexico.¹ The rules for running them and sharing shortages, the 2007 interim guidelines and the 2019 drought contingency plans, expired with 2026.³ After the lowest snowpack on record in the winter of 2025 to 2026, both lakes reached record lows in August 2026.^1,2 When Interior adopted its decision that month their combined contents were 12.5 million acre-feet, the lowest since Lake Powell began filling in 1963.³ Powell's water year to September 2026 brought a preliminary 3.72 million acre-feet of unregulated inflow, 39% of average, and Interior cut the year's release from Powell from 7.48 to 6.0 million acre-feet while sending extra water down from Flaming Gorge reservoir.^5,7

The seven states could not agree on new rules, even after the Interior Secretary convened their governors.³ On 21 August 2026 the Interior Secretary signed a ten-year decision framework to 2036 and the first set of two-year operating rules, for 2027 and 2028, in force from 1 October.^3,11 The three Lower Basin states lose 1.25 million acre-feet a year in 2027 and 2028.^2,4 Arizona gives up 760,000, California 440,000 and Nevada 50,000, and they are to conserve at least 700,000 acre-feet more through 2028.^2,4 The four Upper Basin states (Colorado, New Mexico, Utah, Wyoming) have no mandatory cut.^13,15 Under Minute 334 of the 1944 treaty, signed on 2 September 2026, Mexico's deliveries fall by 250,000 acre-feet a year in 2027 and 2028.^11,12 Nevada sued to set the decision aside on 24 August,¹³ and Arizona said on 16 October that it was joining the suit, which AZFamily reports asks that the Upper Basin states be made to send their promised water to Lake Mead.¹⁴ The week before Nevada sued, Gene Shawcroft, chairman of the Colorado River Authority of Utah, told Utah legislators that "you can't deliver water that doesn't exist."¹⁵

At the end of September 2026 Powell stood at 3,518 feet and Mead at 1,038 feet.^7,8 Below 3,490 feet Glen Canyon Dam can release water only through its outlet works and cannot make power.^3,4 Reclamation's October 2026 study puts Powell no lower than 3,516 feet over the next year on median inflows, but at 3,497 feet by September 2027 and 3,491 feet by February 2028 in its dry case, which inflows would beat 90% of the time.^7,8

Who needs an answer

• The seven basin states, and the cities and irrigation districts within them, deciding whether to negotiate, sue, or plan for deeper cuts when the next two-year rules are written for 2029.
• The Central Arizona Project and the farms and towns it serves, which takes a cut of about half under the new rules, according to AZFamily's reporting.¹⁴
• Tribes with Colorado River rights. Some settled rights have no pipes to use them, some are unquantified, and a new federal pool can offset certain tribal shortages by up to a quarter.^2,16
• Mexico and the International Boundary and Water Commission, deciding whether 2028 needs further reductions.¹²
• Utilities in seven states that buy Glen Canyon Dam's power, through the Western Area Power Administration, and plan for a dam that may stop generating.^4,10

The domains it chains

Snow in the Rockies becomes the inflow to Powell. Two reservoirs then trade water between the upper and lower basins, and both dams make power from it. Farms and cities draw on the same supply; Utah leaders said some water right holders received as little as 10 to 15% of their rights in 2026.¹⁵ Tribal rights differ widely: the Colorado River Indian Tribes' chairwoman describes theirs as the most senior tribal water rights in the Lower Basin, while other tribes hold settled rights they lack the pipes to use.¹⁶ Below the dams come deliveries and salinity at the Mexican border, and the river's wildlife, for which a new biological opinion covers Glen Canyon Dam's operations through 2036.¹

What a twin should let people try

• Sharing rules: the same shortage split by priority, pro rata across the Lower Basin, by state, or across all seven states, and who gains or loses under each. The federal environmental review modelled several of these.³
• A run of dry years: what happens to both lakes if 2027 and 2028 look like 2026, and whether the 1.25 million acre-foot cut is enough.
• Powell below minimum power pool: how much water can still pass the outlet works, how much power is lost, and what replacing it costs.
• Upstream releases: how long water from Flaming Gorge and the other upstream reservoirs can prop Powell up, and what it costs those reservoirs.
• Cuts by sector: the same volume taken from farms or from cities, and what each does to crops, jobs and household supply.
• The compact dispute: the Upper Basin's yearly flow downstream, set against each state's reading of the 1922 compact.

Where to start

Reclamation's monthly 24-Month Study gives month-by-month inflow, release, elevation and storage for the main reservoirs two years ahead, with a dry and a wet case four times a year.⁸ Reclamation's projections come from models built in RiverWare.⁹ The final environmental review, record of decision and 2027 to 2028 rules are on Reclamation's post-2026 pages.¹ USGS Water Data carries stream gauges across the basin. Who Drinks the River? is a playable, deliberately small allocation model of the basin. The Lower Rio Grande is a neighbouring river under a compact and a court settlement.