It’s a scenario no one could have believed was likely, even two weeks ago.

During one of the wettest seasons on record in Northern California, Santa Barbara County’s South Coast is at risk of losing a valuable supply of state aqueduct water it is storing in the San Luis Reservoir in the San Joaquin Valley.

More even than the money, officials say, the loss of that water — a supply large enough to meet the needs of more than half the South Coast for a year — would be a significant blow. Lake Cachuma, once the main water source for the South Coast, has barely begun filling up from the recent rains.

The ground was so dry after five years of drought that very little runoff flowed into the lake, and Cachuma is at only 9 percent capacity.

“This is sort of the ‘perfect storm’ for water managers,” Bob McDonald, general manager of the Carpinteria Valley Water District, told Noozhawk.

“We have reservoirs that are spilling up north and a reservoir that’s not filling at all in our local watershed. It’s not something we want to see.”

Beginning in 2015, South Coast water agencies purchased $14 million worth of California Aqueduct water on the “spot” market and stashed it in 12,700-acre San Luis, one of the largest reservoirs in the state.

The agencies are paying $20 million yearly in fixed costs for the aqueduct branch to Cachuma from Kern County, but they bought extra supplies because annual state water allocations were being cut to 37 percent, on average, in the drought.

According to the Central Coast Water Authority, the agency that operates the State Water Project aqueduct branch, the South Coast today has nearly 18,000 acre-feet of state water in storage at San Luis, carried over from the past two years.

San Luis — located near Los Banos in Merced County — is an artificial, “off-stream” reservoir and has rarely, if ever, physically spilled.

But under state and federal rules, state officials say, any carryover water stored in San Luis will vanish from the books and be relabeled as 2017 aqueduct supply if the reservoir fills to the brim. And if the extreme wet weather continues in Northern California, they say, San Luis could fill by Feb 1.

On Friday, Craig Trombly, who oversees aqueduct contractor agreements for the state Department of Water Resources, said the state could not make an exception and allow South Coast agencies to retain carryover water in San Luis if the reservoir fills.

But he said the state was working closely with the Central Coast Water Authority to find a way to save as much South Coast carryover water as possible, potentially by moving it to underground basins elsewhere in California.

This has often been done before, Trombly said, but never on such short notice.

“We’re doing everything we can within the contract to see if we can get that water out of there,” he said. “We’re making it up day by day, hour by hour. You just never know when the water patterns are going to change, and they changed pretty ferociously in the past several weeks.”

Agencies such as the giant Metropolitan Water District of Southern California are already moving their carryover supplies out of San Luis and parking them in underground basins, Trombly said.

One seemingly obvious solution — pumping all of the South Coast’s carryover water out of San Luis and into Cachuma — is off the table because the pipeline into the lake is too small.

Enlarging it would be an expensive, long-term project.

The risk at San Luis is particularly acute for the Montecito Water District, which is storing 8,200 acre-feet of carryover water there — more than a two-year supply for the community of 9,000 residents. About half of the Montecito carryover is supplemental state water that the district purchased for more than $1 million on the spot market.

“This is an unprecedented situation,” MWD board president Richard Shaikewitz said at a special meeting that was hurriedly scheduled last Monday. “Do we want to gamble it isn’t going to happen? Does it make sense to do nothing?”

None of the immediate alternatives seemed very satisfactory.

Ray Stokes, executive director of the Central Coast Water Authority, told the Montecito board it could store its carryover water in an groundwater banking program managed by the Irvine Ranch Water District in Kern County.

But it would be a two-for-one exchange, he said, meaning Irvine would keep half of the water. On the plus side, Stokes said, if Montecito loses the water, it will likely be able to buy more on the spot market for cheap, given the extreme wet weather to date.

In addition to Montecito, Santa Barbara also faces potentially big losses. The city is storing 4,500 acre-feet of aqueduct water in San Luis, nearly a six-month supply for its population of 90,000.

“Reason has to prevail here,” said Joshua Haggmark, Santa Barbara water resources manager.

“This is goofy. It would blow me away if we can’t resolve this when a good portion of the state is not in a drought right now.”

The Goleta Water District has a four-month supply in storage at San Luis, and Carpinteria has a five-month supply there.

Solvang would be affected, too, if San Luis fills up. In the absence of any downstream releases from Cachuma, the city is counting on its carryover supply in San Luis to replenish its river wells, said Matt van der Linden, the City of Solvang’s director of public works.

The wells, which represent a third of the city’s water supply, could go dry within two months, he said.

“We’re caught in the worst of situations,” van der Linden said.

Noozhawk contributing writer Melinda Burns can be reached at Follow Noozhawk on Twitter: @noozhawk, @NoozhawkNews and @NoozhawkBiz. Connect with Noozhawk on Facebook.