With long-term severe drought continuing to take a toll on the Colorado River, the federal government is expected to announce on Monday that it will retain some water in one of the river’s major reservoirs to temporarily stave off what it called increased uncertainty in water and electricity supplies.

The anticipated decision to keep more water in Lake Powell on the Arizona-Utah border, rather than releasing it downstream to the other major reservoir, Lake Mead near Las Vegas, comes as both are at record-low levels after 20 years of drought.