Native American tribes in the Colorado River basin already have legally quantified rights to roughly one-fifth of the river’s flow, according to a new report from the non-partisan Colorado River Research Group. CCRG said that tribal water rights are a misunderstood and underpublicized facet in dealing with water shortages in the Southwestern United States. Of the seven Colorado River basin states, signatories to the Compact of 1922, the so-called Law of the River, only California and Colorado have larger paper rights to water than the tribes.