Nick Giese heads out to fish on Southern California’s Lake Cachuma. With the reservoir more than 90 percent below capacity, the surrounding region soon will face a water crisis. (Darryl Fears/The Washington Post)

LAKE CACHUMA, Calif. — At the marina Monty Keller manages amid sloping mountains here, business is down by half. For hours every workday, he stares sadly at the reason.

Lake Cachuma, a giant reservoir built to hold Santa Barbara County’s drinking water, has all but vanished in California’s historic drought. It reached an all-time low this summer — 7 percent capacity, which left a thick beige watermark that circles the hills framing the lake like an enormous bathtub ring. “We’re just amazed,” Keller said.

Under a sky that hardly ever delivers rain, the lake will only continue to fall, putting nearly a half-million county residents in an ugly situation. As early as January, the depth is expected to be too low to distribute water.

Barring a winter miracle of massive snows and rains extending into April, weather that has forsaken Southern California for more than five years, there will be “no water available next year from the reservoir,” said Duane Stroup, deputy area manager for the south-central region of the federal Bureau of Reclamation.

The entire Santa Ynez Valley will then face a future without water. The 3,000-acre reservoir supplies half of what the valley needs to recharge an underground aquifer that nearly every household, business and farm uses to pump water.

As Lake Cachuma dwindles, the municipalities nearby likely won’t have enough water in the spring even with restrictions on water use. (Darryl Fears/The Washington Post)

“I don’t know what will happen if we get the same amount of [precipitation] we got this winter. The wells will go dry, and they will fail. There are people in agriculture that will be required to fallow crops,” meaning destroy them, said Bruce Wales, general manager of the Santa Ynez River Water Conservation District. He predicts the area could one day resemble the Central Valley to the east. Residents there couldn’t wash or flush after 2,000 wells recently went dry, and the state has been forced to provide huge tanks and water to hundreds of homes.

The cities of Solvang and Buellton are making plans to tap alternative water sources. The community of Montecito is scrambling to buy whatever the state and private vendors can provide. Next door, Santa Barbara is strongly considering a total ban on outdoor water use as it rushes to start operation of a desalination plant that will turn Pacific Ocean saltwater to drinking water at a rate of 3 million gallons per day.

The water woes have curbed the appeal of coastal towns cherished by the rich and famous and eventually will be a drain on the local economy. On Santa Barbara’s hills, movie stars live in houses shaded by colorful citrus trees. In Montecito, where talk show hosts Oprah Winfrey and Ellen DeGeneres both own property, large estates with long driveways are hidden behind gates. Vacationers flock to the valley to enjoy the scenic landscape and wine.

Southern California has long had an aching thirst. The region is nursed by water funneled through a system of aqueducts and pipes from the Colorado River and reservoirs closer to the northern Sierra Nevada.

That wasn’t enough for growing Santa Barbara County, which sits northwest of Los Angeles. After a bad drought in the middle of the last century, Lake Cachuma was created in 1953 behind the Bradbury Dam, with an elaborate tunnel and conduit to move water to intake plants throughout the county and an aquifer in the valley. The reservoir took five years to fill.

Because it’s a major drinking water source, swimming was never allowed, but the lake was stocked with trout, coy and other fish for recreational anglers. Austin Snider remembers the lake “at its highest point,” nearly halfway up the mountains, when he arrived at the marina as the new mechanic in 2011.

Marina manager Monty Keller looks out at Lake Cachuma. There’s little marina business these days as the reservoir keeps dropping during California’s historic drought. (Darryl Fears/The Washington Post)

“I’ve watched it go down every year since,” he said recently, standing on a bank about 30 feet below what would have been the water’s surface.

Fearing the worst, local water suppliers ordered everyone to cut 35 percent of their monthly water use a year ago. The strain of strict conservation is starting to show. “Customers describe it as having drought fatigue,” said Fray Crease, the county’s water agency manager.

In Santa Barbara’s San Roque neighborhood, where lemon and orange trees abound, some homeowners also call it an injustice. They say they dutifully cut back, even as lawns went brown, but construction projects that daily use thousands of gallons of water have been allowed to proceed.

The city’s website says dozens of building permits are still being considered. Goleta, a neighboring city of about 30,000, mulled a proposal to build 60 homes worth as much as $1 million before recently rejecting it. Some questioned why such plans are even considered in a drought.

“I understand the frustration,” Crease said. “If you’re doing your best to conserve and a house goes up across the street, it’s difficult . . . to understand that.”

A.K. Sinha, a retired Virginia Tech geology professor who recently moved to Santa Barbara, wonders why state and local officials seem so unprepared. “My major point is, droughts will come and go, and you can’t come up with a solution for it?” he said.

Santa Barbara is spending $61 million to bring the desalination plant online, a move expected to provide 30 percent of its water needs. The plant was built 20 years ago during another drought, but when rains returned it was mothballed before it began operating.

That shouldn’t have happened, Sinha argued as a landscaper prepared his lawn for flowers. “Instead, they should’ve built a second one,” he said. “Look at Israel. They have God knows how many desalination plants.”

Desalination is a marvel of technology, but some scientists say it’s also an environmental hazard. Pipes that pull in saltwater through tiny holes harm marine animals, and the briny water pumped back into the ocean after purification is pollution. In addition, the massive amounts of electricity a plant requires is both costly and a significant source of carbon emissions.

Regardless, Sinha appears to have a point. “The future of water supply in southern California is desalination and conservation and recycling,” Crease said. “I think it’s a little bit of everything.”

Along Lake Cachuma, Keller clings to hope for its rebound. Overall visitation at the Cachuma Lake Recreation Area is down 20 percent. The general store his wife, Beverly, manages is often empty.

“If we end up closing the park, we’d both be out of a job,” he said. “That would really suck.”

A silvery sun hung in a clear blue sky on a recent Monday, but no boats were on the water and there were no sales at the marina. Finally, a single customer, Nick Giese, arrived.

Giese descended the steep stairs to a fishing boat, well past the high-water mark for the lake. “You mean the pond?” he quipped. Rain had better come, “else we’re all in trouble,” he said. “I might have to think about moving.”

A soft drizzle had fallen twice in the previous week, but the bone-dry ground absorbed it before any reached the reservoir.

“Sad little rains,” said Snider, the marina mechanic, as he kicked dirt that should have been deep underwater. “We’ve had sad little rains for six years.”