Lake Mead, the largest reservoir in the United States, passed a scary threshold last week.
With the worst drought in recorded history continuing in the Colorado River Basin, Mead's level fell below an elevation of 1,075 feet above sea level.
That number may sound arbitrary, but here's why it's a big deal: If as expected, projections in August do not show the reservoir rising back above the threshold, the first-ever shortage in the basin would be declared by the federal government. And as a result, Arizona, Nevada and Mexico would likely see substantial reductions in their deliveries of Colorado River water.
