In the coming days, Lake Powell, a major reservoir on the Colorado River, is expected to drop below a critical threshold, a sign of the water stress facing the region amid a prolonged drought, warming temperatures and changes in how water cycles through the environment.

Forecasters with the U.S. Bureau of Reclamation, the federal agency charged with managing much of the West’s water infrastructure, expect Lake Powell to fall below a key low-level water mark within a matter of days.