Environment
Irvine Lake drawdown starts Oct. 26 ahead of dam rebuild
Orange County's largest freshwater lake will be lowered in phases before a multiyear rebuild of Santiago Creek Dam's spillway, outlet tower and earthen embankment.
Irvine Ranch Water District is preparing to reduce Irvine Lake's water level beginning October 26, with the reservoir expected to be fully dewatered next summer so contractors can modernize the nearly century-old Santiago Creek Dam, SFGATE reported October 20.
Drawdown begins: October 26, 2026
Major construction: 2027–2030
Project: New spillway and outlet tower, plus embankment reinforcement
Why the lake is being lowered
IRWD says a comprehensive assessment found that the dam remains operational but could be made safer, while the existing outlet tower and spillway are nearing the end of their useful lives. The planned work will replace those structures, strengthen the earthen dam and improve seismic performance and flow control.
The district estimates construction will run from 2027 through 2030. It says the finished project will restore about 3,700 acre-feet of storage capacity, improve local stormwater capture and extend the reservoir's useful life.
Recreation and environmental review
Irvine Lake is also a popular shoreline-fishing destination. SFGATE reported that the water district is consulting fisheries experts and the California Department of Fish and Wildlife about fish management during the drawdown. The Santa Ana Regional Water Quality Control Board is scheduled to consider the project's water-quality permit at an October 23 public hearing; its notice identifies temporary impacts associated with dewatering the lake.
Original reporting and official records: Read the SFGATE report → · View the IRWD project page → · Read the state hearing notice →