Irvine Ranch Water District said on May 28 that crews will begin draining the 750‑acre Irvine Lake at the start of this month, lowering the water level from 735 feet to 720 feet and cutting the stored volume from 2,800 to 300 acre‑feet.
The 93‑year‑old Santiago Creek Dam, classified as an Extremely High hazard by the California Division of Safety of Dams, will receive a new concrete spillway, reinforcement of its earthen core, and a replacement outlet tower. The upgrades aim to raise the lake’s design capacity to 28,000 acre‑feet and mitigate risks highlighted by recent inspections.
Anglers have lodged formal appeals with the state water‑quality board, demanding a plan to relocate non‑native white sturgeon and other stocked species before the lake dries. The water district confirmed it is coordinating with the California Department of Fish and Wildlife to move the fish and will allow shoreline fishing to resume once the reservoir is refilled.
The full drawdown is scheduled for next summer, after which construction will last roughly five years. Once the dam is completed, the lake will return to its original capacity, enabling the district to capture more storm‑water and secure Orange County’s water supply for decades.