Colorado river crosses from the US into Mexico. Its water is diverted to irrigate the Mexicali Valley, one of Mexico's most fertile agricultural lands. This diversion and other dam projects significantly reduce the flow and has severe ecological consequences in the Colorado River Delta and the Gulf of California. Multiple US states and the federal govt work together with the Mexican govt to negotiate an agreement. Known as Minute 319, it permits Mexico storage of its water allotment in U.S. reservoirs during wet years.