Castaic Lagoon, also called the Lower Lake, is the smaller of the two reservoirs inside Castaic Lake State Recreation Area in the community of Castaic, in northern Los Angeles County. The land belongs to California State Parks, but Los Angeles County Parks and Recreation runs the park day to day. The lagoon sits directly below Castaic Dam and covers about 197 acres with roughly 3 miles of shoreline. The California Department of Water Resources releases water from the upper reservoir to hold the lagoon at a steady level for recreation, and the outflow continues south as Castaic Creek.

From Interstate 5, take the Lake Hughes Road exit in Castaic and follow the signs to the main park entrance at 32132 Castaic Lake Drive. The gate kiosk takes cash or card, and bills over $20 may not be accepted. Paved lots line the west shore of the lagoon, and the swim area is a short walk from the parking and restrooms. The west side also has shaded picnic grounds, playgrounds and trailheads, while the east side holds the fishing pier, a 24-hour fishing area and the hand-launch ramp.

Swimming is allowed only at the designated swim beach on the west shore, and only while lifeguards are on duty. The beach is sand that turns to gravel and rock at the water line, and the swim zone is marked with buoys. The lagoon reaches about 70 feet at its deepest, so stay inside the lines. The season usually runs from Memorial Day weekend through Labor Day. In recent seasons the beach was staffed Wednesday through Sunday from 10am to 6pm, and the whole park is closed Mondays and Tuesdays. Dogs must stay leashed and are not allowed on the beach or in the water.

Entry to the swim beach itself is free. The county charges a vehicle entry fee of $15 per day, or $8 for seniors 65 and over and disabled visitors. Castaic Lake does not honor the annual California State Parks pass, but the State Parks Distinguished Veteran Pass is accepted for vehicle entry. The lower lake is open 6am to 7pm on its operating days.

Check conditions before you go. On August 7, 2026, the county closed the Lower Lake, including the swim beach and the Cali Splash inflatable water park, while fire crews used the area as a base camp for the Ridge Fire. No reopening notice had been posted as of early October 2026, and the swim season would have ended by Labor Day in any case. The Department of Water Resources tests both lakes for toxic blue-green algae. Past danger advisories and closures hit the upper reservoir while the lagoon stayed open, but the state listed caution advisories for Castaic Lake in early 2026, so read the posted signs. Quagga mussels were found in the lagoon in 2024, and every boat has to be cleaned, drained and dried. The state also has a fish consumption advisory for mercury and PCBs in both lakes.

Only hand-powered, sail and electric-motor craft are allowed on the lagoon, which keeps it quiet for kayaks, canoes, paddleboards and float tubes. In summer the county runs kayak and paddleboard clinics and a Junior Lake Lifeguard program for kids, and the nonprofit Friends of Castaic Lake helps with events. Trails for hiking, mountain biking and horseback riding start from the west side of the lagoon. The 60-site lagoon campground was damaged in the January 2025 Hughes Fire and has been closed for repairs, so confirm it is open before planning an overnight trip.