Consumption of Colorado River water is outpacing nature’s ability to replenish it, with the basin’s reservoirs on the verge of being depleted to the point of exhaustion without urgent federal action to cut use, according to a new analysis from leading experts of the river.

The analysis, published Thursday, found that if the river’s water continues to be used at the same rate and the Southwest sees another winter as dry as the last one, Lakes Mead and Powell—the nation’s two largest reservoirs—would collectively hold 9 percent of the water they can store by the end of next summer.

After enduring decades of overconsumption of the river’s water, the lakes would have just under 4 million acre feet of water in storage for emergencies and drier years when demand can’t be met. Every year, roughly 13 million acre feet is taken from the river for drinking water and human development across the region, with conservative forecasts estimating roughly 9.3 million acre feet of inflow next year.

The report is stark in its assessment of the situation: Current Colorado River levels require “immediate and substantial reductions in consumptive use across the Basin” or Lake Powell by 2027 would have no storage left and “would have to be operated as a ‘run of river” facility” in which only the inflow from the river could be released downstream.