Just one day after U.S. officials declared the first-ever water shortage on the Colorado River, the Metropolitan Water District of Southern California issued a water supply alert calling on the region to conserve vital resources and prepare for continued drought.

The MWD supplies water to approximately 19 million people across six Southern California counties and is one of the largest water distributors in the nation. The decision by its board Tuesday marks the first time in seven years the agency has issued an official supply alert — the third of four escalating phases in its water supply framework.

The declaration marks a call for regional agencies and consumers to voluntarily reduce their water consumption in order to mitigate the need for more severe restrictions.