LAKE MEAD, Nev. -- When you head out on Nevada's Lake Mead, the first thing you notice is a white line. That's where the water used to be.

What did this look like a decade ago?

This was all underwater, said Pat Mulroy, the general manager of the Southern Nevada Water Authority. I mean boats were everywhere. There was a whole marina here.

Mulroy said that the drought began 14 years ago. Satellite photos show the Colorado River, which feeds Lake Mead, is drying up -- so the lake is rapidly shrinking. Islands are growing, and boats are floating far from where they once were.

It's a pretty critical point, Mulroy said. The rate at which our weather patterns are changing is so dramatic that our ability to adapt to it is really crippled.

Lake Mead was created by the Hoover Dam in 1935. It provides water for 20 million people in southern Nevada, southern California and Arizona. Since 2000, the lake has lost 4 trillion gallons of water.

The bathtub ring is going to get bigger. Lake Mead is expected to drop at least another 20 feet this year. If it does that could trigger automatic cuts to the water supply for Nevada and Arizona.

That would hit Las Vegas hard. Ninety percent of the area's water comes from the lake. At least one of the city's two intake pipes could soon be above water. So to save the water supply Nevada is rushing to build a third intake even deeper.

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