LOS ANGELES (AP) — A major Southern California water agency has declared a water supply alert for the first time in seven years and is asking residents to voluntarily conserve.

The Los Angeles Times reports that the board of the Metropolitan Water District of Southern California took the step Tuesday, hoping to lessen the need for more severe actions such as reducing water supplies to member agencies.

The move comes a day after U.S. officials declared the first-ever water shortage on the Colorado River, a key water source for Southern California.

“This is a wake-up call for what lies ahead," said Deven Upadhyay, chief operating officer for the district that supplies water to 19 million Californians.

“We cannot overstate the seriousness of this drought," he said. "Conditions are getting worse, and more importantly, we don’t know how long it will last.”

California Gov. Gavin Newsom last month asked Californians to scale back water use and many of the state's counties, mostly in Central and Northern California, are already under a state of drought emergency.

Concern about water supplies spread to the state's heavily-populated southern region following a winter of low precipitation and shrinking reservoirs throughout the West.

Newsom on Tuesday said he may put mandatory water restrictions in place in the coming months, the East Bay Times reported.

“At the moment, we’re doing voluntary,” he said. “But if we enter into another year of drought — and as you know our water season starts Oct. 1 — we will have likely more to say by the end of September as we enter potentially the third year of this current drought.”

The Metropolitan Water District of Southern California receives about half its water from the Colorado River and State Water Project.

Water levels in Lake Mead, the largest reservoir on the Colorado River, were at about 35% of capacity on Tuesday. The State Water Project, which collects water from rivers and tributaries, has already reduced the Southern California district's allocation to 5% and next year the amount could be zero, officials said.

Scientists say climate change has made the American West much warmer and drier in the past 30 years and will keep making weather more extreme.

Glen MacDonald, a University of California, Los Angeles distinguished professor of California and the American West, said even if precipitation returned it would not likely be enough to keep pace with the loss of water through evaporation due to rising temperatures.

That has the potential to not only turn California lawns brown but could also affect the nation's food supply, which relies heavily on the state's farmlands, MacDonald said.

“We are living in the perfect drought, right now,” he said. “It’s unfortunate, but we kind of have seen this coming.”

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