Summers in the American West are always hot and dry. But this year is even hotter and drier than usual in fact, it's the worst drought in a century - a perfect excuse for an escape to a nearby cool river or lake. But the drought is having a major impact in those places as well, as Mitch Teich discovered at Lake Mead, the largest man-made reservoir in the United States.

Even in a normal year, Lake Mead looks remarkable. Its azure blue waters leap out in contrast to the arid landscape of the surrounding Arizona and Nevada desert. But this year, Lake Mead is sporting another remarkable feature that not even the tour guides can ignore.

A tour guide tells visitors the lake can hold 35 trillion liters of water. "But you can see we're not at our full-storage capacity right now because of that big white line," he says, pointing up more than five stories above the surface of the lake, circling it like a giant bathtub ring. It's so white because the Colorado River water that flows into Lake Mead is full of calcium from the Rocky Mountains. It's so visible because of the drought.

Gary Bryant manages Hoover Dam, the huge dam just south of the lake that provides flood control, water storage and hydroelectric power for the southwestern states. He says the entire river system is receiving only about a quarter of its usual inflow, and the water level has dropped more than 10 meters in the past two years. But Mr. Bryant says Lake Mead's primary mission, water storage, is not in danger yet.

"So we have about two to three years' worth of water left in the reservoirs, even if we never got any water into them and you always get some water. So we've got enough water to provide the southwest with the water they need," he explained.

But water storage is far from the minds of Kelly Bowen and Ann Iocca, two of the millions of people who come to Lake Mead each year to boat, water ski or just cool off.

As Ms. Iocca backs up a truck with a trailer bearing a new Jet Ski, most of the ramp she's using would have been under three meters of water a year ago. Today's she's inching down concrete that has been submerged for decades. Her friend Kelly Bowen says the drop in water levels means less carefree fun on the Jet Ski.

"Well, you don't go speeding around like you used to anymore," he said. "There's a lot of places [obstacles] that are unmarked that are just below the surface. There are even some exposed rocks that are above the surface that are not marked. And you have to be very careful."

Probably the biggest effect of Lake Mead's drop has been economic. By the beginning of June, tourism was already down 10 percent for the year, and shows no sign of improving. Operators of Lake Mead Marina have been forced to physically move their docks and equipment several times, chasing the water as it recedes.

"Any time you move a marina out, you have to move all the lines - for the gas, for the fuel dock, and for the sewage, and everything's got to all be moved out," said Karla Norris, of the National Park Service. "It's very time-consuming and costly, and they're having to do this every few weeks."

And as news of the drop in water levels circulates, there are fears the boaters will stay away. "If it's not deep enough, of course you can't launch it," said Les Fry of Henderson, Nevada, "and it doesn't look like it's deep enough."

Normally, Mr. Fry tries to get on the water at least once a week, but he says this year is different. "I mean, here, you look at Lake Mead Marina, there's nobody here today, and normally, you'd have quite a few boats launching. I think a lot of people are aware of the fact that the lake level is so low, that it's so difficult to launch a boat," he said.

But Mr. Fry says he'll keep looking for a deeper harbor. And if he does find one and make it onto Lake Mead, the Park Service's Karla Norris says he may see features along the lakeside that haven't been seen since the 1930s, when Black Canyon was flooded and Lake Mead was created.