Experts say the critical reservoir system is careening toward a breaking point as the US west’s climate warms and dries

Lake Powell, the US’s second-largest reservoir, threatens to plunge to unprecedentedly low levels this year after a historically bleak snowpack failed to raise its water level, scientists and water experts have said, adding renewed urgency to stalled talks over how to conserve a water source depended on by tens of millions of people in the US south-west.

The 185-mile Colorado River reservoir currently stands at about 22% of its capacity,