…Nasa, which monitors changing water levels, is warning that the western United States is now entering one of the worst droughts ever seen.
"With climate change, it seems like the dominoes are beginning to fall," Nasa hydrologist JT Reager told the BBC.
"We get warmer temperatures, we get less precipitation and snow. The reservoirs start drying up, then in a place like the West, we get wildfires".
These consequences are beginning to have "stronger and stronger impacts," Mr Reager said.
"It's like watching this slow motion catastrophe kind of unfold".
Farmers are already feeling the pain. About 75% of the water from Lake Mead goes to agriculture.
Over a third of America's vegetables and two-thirds of its fruits and nuts are grown in California. But tens of thousands of acres lie idle because farmers can't get enough water to grow crops.
The impact may be seen on grocery store shelves next year, Bill Diedrich, a Californian farmer, told BBC. This season's produce shows up at shops next season, he explained as he showed his bone-dry fallowed fields. Typically, he would plant tomatoes for canning on this field but he didn't have enough water.
Mr Dietrich said he hoped his children would have the opportunity to carry on farming in California in the future.
But, he said, "I don't know what the odds of that are"…