Irvine Lake

Water Storage at Irvine Lake

Since it was originally constructed in 1933, the primary purpose of Irvine Lake (Santiago Creek Reservoir) is to store water for the benefit of the surrounding communities – initially to provide irrigation water for local farms, and more recently to satisfy water demands primarily for urban needs. Irvine Ranch Water District uses water from Irvine Lake as a source of water for two purposes:

• Non-drinking purposes, such as irrigation for avocado orchards.
• For the Baker and Howiler water treatment plants, which process drinking water for an estimated 85,000 homes in Orange County. 

IRWD balances the benefits of storing water in Irvine Lake to ensure customers have a reliable supply of water with minimizing evaporation of water from the Lake. When the water level in Irvine Lake is high, the rate of evaporation increases dramatically with the increased surface area of water. One other key consideration for managing water levels in the Lake is preserving the ability to capture rainwater from the surrounding hills that will flow into Irvine Lake. Capturing this fresh water in Irvine Lake at no cost can help reduce the cost of providing drinking water to customers.

Water Quality at Irvine Lake

As a source of drinking water, water quality at Irvine Lake is important. Rainwater runoff from the local watershed fills the lake. In order to ensure water quality remains high and supports uses, IRWD conducts extensive routine monitoring of the lake. The Irvine Lake watershed is also subject to sanitary surveys every 5-years to determine if there are any threats to water quality present in the watershed. The most recent survey was completed in 2019, and it found that the local watershed is predominantly rural with the primary threats to water quality from wildfires and septic systems.

During years with less rainfall, IRWD adds untreated imported water to Irvine Lake purchased from the Metropolitan Water District of Southern California. MWD provides drinking water to communities throughout Southern California, and they conduct extensive monitoring of federal and state regulated constituents as well as many additional water quality parameters. 

Fishing at Irvine Lake

Irvine Lake serves primarily as a water resource facility, with limited shoreline fishing. 

At IRWD, we support recreation in Orange County and take pride in offering opportunities for our customers to explore the outdoors and learn about their environment. Through a cooperative agreement with IRWD, the County of Orange manages recreation at Irvine Lake. For details on fishing, please contact OC Parks.