State officials warned Monday that low runoff in rivers could require even senior water rights holders to reduce consumption this summer.
The notice by the State Water Resources Control Board, which regulates water rights, is informational only. But it is a warning that curtailment orders could follow if water users don't begin conserving, said Les Grober, assistant deputy director for water rights at the board.
Even so-called "riparian" and "pre-1914" water rights, the most senior category, could be affected. Such curtailments have not occurred since the drought of 1976-77, considered the most severe in modern times.
"This is really a heads-up for a potentially critical condition," Grober said.
The notice was primarily aimed at farm water users in the Sacramento Valley, who generally hold the most-senior water rights. It came with a two-page list of conservation practices for "immediate consideration."
The Northern Sierra Nevada, which provides much of California's water supply via snowmelt, saw the driest January-through-June period in 90 years.
Reservoirs in the region, the largest in the state, are at about 80 percent of capacity and shrinking rapidly.
The notice can be found online at: http://ht.ly/n23fj.
Contact The Bee's Matt Weiser at (916) 321-1264. Follow him on Twitter @matt_weiser.