The Colorado River Compact is a deal between seven western states who get rights to parts of the Colorado River. The agreement was first approved by President Hoover in 1922 and there have been some amendments after that.
The compact divides the river into two sections:
The Upper Basin includes Colorado, New Mexico, Utah and Wyoming. The Lower Basin made up of Nevada, Arizona and California. The Colorado River Compact divides about 15 million acre-feet of water between the two basins, if that much water is actually available.
According to the Water Education Foundation, after the Lower Basin states and Mexico receive their shares of the river, then the Upper Basin states keep the remaining water supply in the Colorado River. Water is measured and distributed to the Lower Basin states at Lee’s Ferry, which is on the Arizona and Utah border and shown in the picture above.