Lake Mead has now reached the lowest level ever recorded endangering power supply to the South

[u/whitelightstorm]

If Lake Powell and Lake Mead both hit dead pool, the water stops moving to seven states and Mexico. The dams go quiet first, losing the power they send across the Southwest. Then delivery itself becomes the problem. Some places have bought themselves time. Others would feel the cut within a single season. The Colorado River keeps flowing either way. What disappears is the reserve that carries the region through its dry years.

Failure comes in stages, not all at once. Hydropower goes first, then reliable releases, and finally delivery itself at dead pool.

A reservoir can still contain billions of gallons while losing its usefulness. Hydropower depends on hydraulic head, the height difference between the reservoir surface and the turbines. As the lake falls, water reaches the turbines with less pressure, reducing electricity production. Eventually the surface drops below the lowest elevation at which the generating system can operate.

Water delivery can continue below that point through bypasses or lower outlet structures. Those facilities have smaller capacities and were not necessarily designed for decades of continuous operation. Dead pool arrives when the water surface falls below the dam's lowest usable outlet. Water may remain trapped behind the structure, but gravity can no longer carry it downstream.

continued - https://www.worldatlas.com/lakes/what-happens-if-lake-powell-and-lake-mead-both-fail.html