https://abcnews.com/amp/US/lake-powell-reaching-critically-low-elevation-levels-nearing/story?id=134659320
"The reservoir could reach a "dead pool" when its elevation drops to 3,370 feet, at which point water can no longer flow past Glen Canyon Dam by gravity.
In a dead pool, about 240 feet of water would be trapped at the bottom of the canyon, unable to flow to millions of people who rely on it in Arizona, California and Nevada, the Lake Powell Chronicle reported..."