For the Standing Rock Sioux Tribe, whose lands straddle the North and South Dakota border, river water means drinking supplies. For Illinois farmers, it's irrigation for their crops.
Rivers also power hydro-electric plants, provide recreation for boaters and give coal companies inexpensive access to export markets with barges to New Orleans.
Balancing these competing demands on the nation's water resources has never been easy. Global warming, linked to near- record low water levels on the Mississippi River this year as well as last year’s severe floods along the Missouri River, is making the task even harder.
"You end up pitting one constituency against another, and then you mud-wrestle over the right balance," Ben Grumbles, president of the Washington-based environmental group U.S. Water Alliance, said. "Climate change means water change."