Five of the driest years on record have left Lake Powell, the giant impoundment on the Utah-Arizona line, two-thirds empty.
Meanwhile, record precipitation this winter has helped produce a dramatic rebound in Lake Mead, Powell's equally large downstream sibling, which is now nearly two-thirds full.
To help restore balance to the system, Utah, Colorado, New Mexico and Wyoming want the Bureau of Reclamation to capture more water than planned behind Lake Powell's Glen Canyon Dam. They plan to make that request next week.
"It's just common sense at this point," says Rod Kuharich, executive director of the Colorado Water Conservation Board.
But Kuharich said consensus among the seven states is unlikely by federal officials' Tuesday deadline.
That would leave Norton to make a decision in early May.
Upper Basin states want Lake Powell to fill because the lake plays a critical role in providing water for downstream users especially during dry years.
If the lake empties, California, Nevada and Arizona, which have a senior claim on the Colorado River, would be able to take water from the river that Front Range residents now use.
"It's our protection," Dave Merritt, chief engineer of the Colorado River Water Conservation District in Grand Junction, said of Lake Powell.
The debate was cast last fall when officials, wary that the drought could deepen, agreed to an unprecedented midyear review of Glen Canyon's operations.
Lower Basin officials argue no change of course is needed. They point out that the reservoir's annual operating plan, which is set each September, assumed continued drought in the Upper Basin would reduce runoff into the reservoir to 77 percent of normal. Instead, runoff is forecast to be 107 percent of normal.
"That's 30 percent better than the estimate used in setting the operating plan," said Herb Guenther, director of Arizona's Department of Water Resources.
In addition, Lower Basin officials say, the two reservoirs are headed in opposite directions.
The runoff season, which is just starting, will raise Lake Powell's level to 49 percent of capacity by summer's end.
Meanwhile Lake Mead's level will drop to about 54 percent by the end of the year, officials said.
"So they'll be getting pretty close equalizing on their own," said Dennis Underwood, chief executive of Southern California's Metropolitan Water District, which serves Los Angeles and San Diego.
But Upper Basin officials are frustrated by the Lower Basin's reluctance to let Powell fill.
After all, they argue, Lake Powell's water is destined for California, Arizona and Nevada anyway. Refilling the reservoir means more reliable supplies to the lower basin if drought returns.
A fuller Lake Powell produces more power, and hence more revenue, from the turbines in Glen Canyon Dam.
And, because Powell is higher in elevation, the vast lake surface loses less to evaporation than Mead, they say.
Lurking below the surface is lingering uncertainty about what next year will bring.
"The drought in the Colorado River basin has eased," said Tom Ryan, a Bureau of Reclamation hydrologist. "We can't say that it's over."
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