Colorado River water managers could be pulled back to the negotiating table as soon as next year to keep its biggest reservoirs from declining further.

The 2019 Drought Contingency Plan was meant to give the U.S. and Mexican states that depend on the river a roadmap to manage water shortages. That plan requires the river’s biggest reservoir, Lake Mead, to drop to unprecedented levels before conservation among all the lower basin states — Arizona, Nevada and California — becomes mandatory. California isn’t required to conserve water in the reservoir until it drops to an elevation of 1,045 feet above sea level.