The Board has long had the authority to adopt “emergency regulation[s]” “to require curtailment of diversions when water is not available under the diverter’s priority of right, or in furtherance of any of the foregoing, to require reporting of diversion or use or the preparation of monitoring reports.”…The Board has utilized its emergency regulation authority to enact regulations authorizing it to curtail water use by classes of water right holders during droughts. Neither section 1058.5 nor any of these regulations contains the limits found in section 1052(a). (citations omitted.)

the court’s decision does not impact the State Water Board’s ongoing drought response actions, including curtailments of senior water rights, which rely on drought emergency regulations. Likewise, it does not impact the board’s authority to take actions against illegal diversions, nor does it preclude the board from taking enforcement measures to protect water released from storage, such as the State Water Project or Central Valley Project.

“Because the Board did not base these notices on the presence (or even possible presence) of stored water in the Delta, the trial court properly concluded that the Board’s authority to act under section 1052(a) could not be upheld on that basis.”