[4] Pacific Gas and Electric constructed its Claremont substation directly above Lake Temescal starting in October of 1921.

As part of the project, Landvale Road was extended as a connecting viaduct with Mountain Boulevard and the Montclair District to the south.

This required the construction of a large concrete retaining wall along the east side of Lake Temescal to support the fill.

Its early amenities included a beach-like shore for swimming, a boathouse built by the WPA, a well established trail around the lake, and numerous picnic benches.

The lake currently supports an artificial recreational beach and is stocked periodically with rainbow trout, largemouth bass, redear sunfish, bluegill, and catfish.

The California Office of Environmental Health Hazard Assessment (OEHHA) has developed a safe eating advisory for Lake Temescal based on levels of mercury or PCBs found in fish caught from this water body.

The park's beach and swim area have periodically closed on and off due to an outbreaks of toxic blue-green algae that is hazardous to humans and pets.