Lake Temescal is a small lake with a long history sitting in a fold of the Oakland hills where Highway 24 dives into the Caldecott Tunnel. Anthony Chabot built the dam in 1868 to supply drinking water to Oakland, and the way he built it is the interesting part: rather than hauling fill, he used hydraulic mining monitors to wash the hillside down into the ravine, then drove herds of horses back and forth across the deposited earth to compact it. The dam held, the technique became the model for his larger dams at Lake Chabot and elsewhere, and the reservoir stayed in the water system until Oakland outgrew it.

In 1936 Temescal became one of the first three parks of the brand new East Bay Regional Park District, along with Tilden and Redwood. The beach, the stone bathhouse and the Beach House at the north end all date from that era and the WPA work that followed. The lake covers about ten acres, sits in a bowl of eucalyptus, bay and oak, and is circled by a flat trail a little over a mile long that makes a pleasant lap without much climbing.

The swim beach is on the north shore, a crescent of coarse sand with a roped-off shallow area and a raft further out. Lifeguards are on duty during the posted summer season, usually from late May through early September, with weekend-only coverage at the shoulders. Outside those hours the beach is closed to swimming. The water is fresh, calm and warmer than anything in the bay, generally in the upper 60s to low 70s by August. The park district tests the water regularly and posts closures when bacteria counts rise or when a blue-green algae bloom appears, which happens most often in late summer during warm still spells, so it is worth checking the swim status page the morning you go.

Parking is in two lots, one off Broadway Terrace at the north end by the beach and one at the south end off Highway 13, and there is a parking fee when the kiosk is staffed in season. The north lot fills early on hot weekends. Fishing is popular on the south end, where the district stocks trout in the cooler months and catfish in summer, and a California license is required for anyone sixteen and over. Dogs are welcome on the trails but not on the swim beach or the lawn.

The setting is a curiosity in itself. The freeway is close enough that you hear it from the water, and the hillside above the south end burned in the 1991 Oakland hills firestorm, which is why the ridge across the lake looks younger than the mature grove around the beach. The sunsets over that burn scar look west across the bay toward San Francisco and the Golden Gate, and the Rockridge shops and BART station are a mile downhill.