LAKE MEAD NATIONAL RECREATION AREA, Nev. — Gail Kaiser has spent much of her life here on Lake Mead, with its crystal blue water pouring into canyons and splintering off like blood vessels into coves and bays, forming the vast reservoir that stretches into two states.

She was just a child when, in 1957, her father took over the marina that has stayed in her family’s hands ever since. The lake, which is part of the Colorado River system and feeds into the Hoover Dam, was designed to fluctuate like a giant bathtub. In her life, she has seen it at its fullest, in the early 1980s, as water gushed over the spillways at the dam.

But more recently, as the area has been in a drought for most of the last 15 years, she has seen the water creep away, with a chalky ring on the lake’s rocky edges marking the heights it once reached. The longtime home of the marina has mostly dried up, forcing a move several years ago to a site 12 miles away. And on a recent morning, crews went to work on the elaborate process, requiring weeks of preparation and costing over $100,000, to ease the marina — with its boat slips, shop and offices — farther out into water.

“We’ve seen some extreme highs and some extreme lows,” said Ms. Kaiser, 61, “and this is the lowest that I remember.”

When it is full, the reservoir, a few dozen miles from the Las Vegas Strip, reaches an elevation of more than 1,220 feet. But last week, Lake Mead broke records, falling to about 1,079 feet, lows not seen since the lake was created in the 1930s. The lake is at only 38 percent of its capacity, and officials warn that the water level will continue to fall throughout the summer, with projections showing an estimated elevation of 1,073 feet by September.

“This is a pretty severe, lengthy drought, and it’s taking its toll,” said Rose Davis, a spokeswoman for the United States Bureau of Reclamation’s Lower Colorado Region.

The Colorado River system directs water to states throughout the region and into Mexico, but years of drought have raised concerns about its sustainability.

Projections show the lake returning to 1,080 feet by the start of next year, but if the water does not rise above 1,075 feet by January, officials will be forced to reduce the amount of the water delivered to Arizona and Nevada. And researchers fear that the drought conditions could linger for years, sharply reducing the snowpack in the north that replenishes the river.

“The Southwest sits in a kind of bull’s-eye of continued warming,” said Thomas C. Piechota, a professor of civil and environmental engineering at the University of Nevada, Las Vegas. “We’ve seen this warming over the last 20 years.”

Some researchers argue that the demands on the lake as a water source leave little flexibility for restoring its supply.

“They have practically allocated every single drop, and for many years they had over-allocated,” said Sajjad Ahmad, who is also a civil and environmental engineering professor at U.N.L.V. “We are operating on the edge. That we know.”

Las Vegas relies on Lake Mead for 90 percent of its water, but after more than a decade of drought, water officials there have taken on a range of measures to adjust to life with a reduced supply.

“We came into the 21st century with Lake Mead essentially full, and over the last 14 years, it has declined about 130 feet,” said John Entsminger, general manager of the Southern Nevada Water Authority. “What we’ve learned here in Las Vegas is it sure looks like the 21st century in the Western U.S. is a time when everyone is going to have to use less water.”

Mr. Entsminger boasted of conservation efforts that reduced water use even as Las Vegas’s population grew, including offering incentives to abandon thirsty green yards in favor of desert landscaping. Since 2002, the water authority said, its net use has fallen by about 30 percent.

The water authority has also added the ability to draw water from Lake Mead at much lower levels, with an intake and pumping facility that will allow it to continue to use the lake as a water source even if the supply becomes too limited to be delivered downstream.

“Lake Mead will be able to sustain Las Vegas for the indefinite future,” Mr. Entsminger said. “By indefinite, I mean hundreds of years.”

As the levels fall on the lake, Ms. Kaiser plans to push the marina farther out in the water at least two more times. The National Park Service is also lengthening ramps so boats can be launched at the 1,073-foot elevation, doing so after an extension about five years ago.

Ms. Kaiser’s fears are less about the falling water level and directed more at the attention paid to it. She remembered the last time stories of record-breaking lows spread just before the relief of an exceptionally wet year in 2011, and what that meant for her business.

“We take phone calls from all over the world from people that think Lake Mead is a mud hole,” she said. “They call and want to cancel their reservation because they heard there’s no water there.”

But the lake, which draws close to seven million tourists a year, is still a blue expanse amid the desert, covering about 242,000 acres and in places plunging nearly 300 feet deep.

And as the water shifts, it has brought new opportunity for exploration. Just last month, the National Park Service issued a permit for a company based in Lake Havasu City, Ariz., to guide divers on tours of a B-29 bomber that crashed in 1948. A few years ago, when the park service issued a permit, the wreckage was at a depth accessible only to highly skilled divers. Now, the water levels make it more easily reachable.

Ms. Kaiser, who has traversed much of the area around the lake over the years, has come across new islands and coves. “We’re seeing things pop up we’ve never seen before,” she said.

“I’ve loved it enough I’ve stayed here all these years,” Ms. Kaiser said in her office with a window looking out at water teeming with the carp and striped bass that crowd the edge of the boardwalk, waiting for tourists to fling popcorn.

“Does it get rough out there sometimes? Absolutely,” she continued. “Is there a new adventure because the water levels change? Absolutely.”

But, she added, “it’s still a big, clear, beautiful lake, and it will remain that.”