The Colorado River is nearing collapse. It’s Trump’s problem now.

A century-old legal framework promises those users more water than there is to go around. The river’s flow has shrunk by about 20 percent over the last century as climate change has made the West more arid. As water has vanished, states have clashed over how to divide up what remains. The core dispute is between the sparsely inhabited mountainous states of the “Upper Basin,” where hay farmers and a few major cities like Denver draw water from the river and its tributaries, and the far more populous “Lower Basin,” which diverts water to support most of the nation’s winter vegetable farmers as well as megacities like Los Angeles and Phoenix.