Lake Mead receives the majority of its water from snow melt in the Colorado, Wyoming, and Utah Rocky Mountains. Inflows to the lake are largely moderated by the upstream Glen Canyon Dam, which is required to release of water each year to Lake Mead. Hoover Dam is required to release of water each year, with the difference made up by tributaries that join the Colorado below Glen Canyon or flow into Lake Mead. Outflow, which includes evaporation and delivery to Arizona, California, Nevada, and Mexico from Lake Mead is generally in the range of , resulting in a net annual deficit of about .