LAS VEGAS (KLAS) — Hoover Dam is home to one of the largest hydropower plants in the United States. And more than half the electricity it produces is sent to California.

But its ability to send that electricity has been dwindling and the reservoir levels at the dam have been sinking to record lows.

On a visit to the dam, it doesn’t take long to see just how low Lake Mead has fallen.

Photos provide a drastic comparison. A picture of the reservoir in November of 2000 shows just how much water has disappeared compared to a more recent view, when the reservoir was at a record low.

“If you look at it on the reservoir here, you’ll see that we’re down about 158 feet from full pool. That’s what we euphemistically call the bathtub ring,” said Doug Hendrix of the Bureau of Reclamation. “I mean, we’ve been creeping down to this level for quite some time … for the last 22 years.”

The bureau, which runs the dam, gave us a tour to explain the problems the drought is causing. And it’s not just the water supply.

It’s the power supply, too.

Lake Mead’s water is used to spin the turbines that produce electricity at Hoover Dam. It’s one of the largest hydropower plants in the United States.

On the back side of the Hoover Dam, you can see the transformer deck. That’s where — once the power is made — it’s sent out so California and other states can use it. But because of the drought, the dam can’t generate as much power as it used to.

“Under full reservoir conditions we can generate about 2,074 Megawatts of power here, enough power for about a million residents,” Hendrix said. “But unfortunately now, we’re down to — because of the lower reservoir conditions — we’re only generating about 66% efficiency these days.”

The Oroville Dam and others in California are suffering similar fates. The Department of Water Resources says Lake Oroville may get so low by the end of summer that the Edward Hyatt Power Plant there might not be able to produce any power at all.

The hydropower problem is just one of many reasons the North American Electric Reliability Corporation (NERC) has put California at a “high risk” of power outages this summer.

“During some hours when electricity consumption is at its highest, or as the solar generation output is reduced closer to the evening hours, there may be a need for system operators to take certain actions,” said John Moura of NERC.

“So yes, our new assessment is warning — creating some caution of elevated risk — that some customers might see some outages in the summer,” Moura said.

And Lake Mead continues to sink lower, setting new records every day.

The two-decade drought has pushed the lake to an elevation of 1068.5 feet as of Monday.

In August, a federal water shortage declaration is expected, which would trigger automatic cuts in water usage in several southwestern states.