The Colorado River, which supplies water to 40 million people across seven US states, is facing an escalating crisis as its two largest reservoirs, Lake Mead and Lake Powell, have hit record-low levels. Hopes that this winter's exceptionally strong El Niño weather pattern might bring relief through increased rain and snowfall are being tempered by experts, who warn that even a best-case wet winter cannot resolve the river's deeper, long-term problems of over-allocation and mismanagement.

Lake Powell recently stood at 3,519.4 feet and Lake Mead at 1,039.6 feet, both record lows, with each reservoir at risk of reaching "deadpool" level, at which point water can no longer flow downstream and hydropower generation is affected. The crisis is compounded by politics, as the century-old compact governing water rights on the river expires at the end of the year, with states having missed deadlines to agree a replacement, forcing federal intervention. While climate scientists say a strong El Niño typically brings wetter conditions to the southern US, including the Lower Basin states of California, Arizona and Nevada, its effect on snowpack in the Upper Basin states, whose meltwater actually replenishes the reservoirs, is far less certain, with past strong El Niño years showing only "normal" snowfall there.