Serious water shortages on the Colorado River could be less than two years away, according to new federal estimates. Yet after 19 years of drought, just 500 farmers in one Arizona county may decide the fate of the entire Southwest: By holding tight to their own temporary water supply, they could stall a conservation plan designed to save the entire region from water shortages.

Pinal County, sandwiched between Phoenix and Tucson, is the third-largest farming county in Arizona and 54th in the nation, generating about $1 billion in annual sales, according to United States Department of Agriculture statistics. Beef cattle and milk generate more than half of that income, with cotton and alfalfa the next largest commodities