For years now, Lake Mead's so-called "bathtub ring" has been a sign of less water flowing into the reservoir. Arizona, California, Nevada and Mexico rely on Lake Mead for their allotments from the Colorado River.
If a shortage is declared, federal guidelines dictate that Arizona take the biggest reductions in the lower basin. University of Arizona Professor George Frisvold explains the immediate challenges a shortage would create for Arizona's agricultural communities.