Quarry Lakes is the East Bay's answer to a hot Fremont weekend: a chain of old gravel pits along Alameda Creek that the East Bay Regional Park District and the Alameda County Water District turned into a 471-acre park with about 350 acres of open water. The swim beach is on Horseshoe Lake at the Niles Beach Swim Complex, a broad crescent of imported sand with a roped swim area, lifeguard towers, outdoor showers, restrooms and a lawn behind it. The park is at 2100 Isherwood Way, between the Niles district and Union City, and the lakes are also part of the water district's groundwater recharge system, so the water level moves with the season.

Lifeguards work weekends and holidays only, in 2026 from May 16 through September 27, 11 a.m. to 6 p.m. Outside those hours the beach is open to wading but the swim area is closed. Parking is $5 per car and swimming is $5 for adults and $3 for kids and seniors, all paid cashless at the kiosk; there are no private concessions and the fees go to the park district. Dogs are not allowed on the beach or in the water. The district posts blue-green algae advisories at the entrance and on its website when a bloom is detected, which happens most summers in at least one of the lakes, so check before you go if you plan to put your head under.

Beyond the beach, the park has four lakes: Horseshoe, Rainbow, Lago Los Osos and Shinn Pond. Rainbow Lake is stocked with trout in the cool months and catfish in summer and is the anglers' lake; a state fishing license plus the district's daily fishing access permit are required. Non-motorized boats and boats with electric motors launch at Horseshoe Lake, and it is a good flatwater kayak spot with a view of the Mission Peak ridge to the east. A network of flat gravel and paved trails circles the lakes for walkers and easy mountain biking, and the Alameda Creek Regional Trail runs along the north edge of the park for 12 miles between Niles Canyon and the bay.

Gravel came out of these pits for close to a century, first for railroad ballast and later for Bay Area construction, before the last operator quit in the 1970s. Conversion to a park ran from 1997 to 2000, and the district marks the 25th anniversary of the opening on November 7, 2026. It is 30 minutes from San Jose and Oakland on a quiet day and considerably more when the beach lot fills, which on a hot Saturday happens before noon. Arrive early, or come on a weekday for a long walk around water you'd never guess was once a hole in the ground.