LA County's Largest Lake Is A Summer Swimming Haven With A Fun Inflatable Aquapark

About an hour's drive from Los Angeles sits the largest lake in LA County, Castaic Lake. The Castaic Lake State Recreation Area is a drinking water reservoir, part of the State Water Project, and one of the project's largest recreational lakes. This incredible lake offers more than 29 miles of shoreline for plenty of ways to cool off during the Southern California summer heat. It is also home to a fun, family-friendly attraction: the Cali Splash inflatable water park.

There are two main bodies of water at Castaic lake: the Upper Lake and the Lower Lake. The Upper or Main Lake is created by the magnificent 425-foot-tall dam, a view in and of itself. This part of the recreation area is reserved for the adrenaline seekers on motor-powered boats, or those keen on casting a line. The Upper Lake is divided into two arms: The east arm is the "fish arm," designated for fishing, and the west arm, the "ski arm," is designated for on-water fun like waterskiing, wakeboarding, and other towable activities. 

The Lower Lake, also known as Castaic Lagoon, is reserved for nonmotorized boating and swimming. The lagoon is the swimming haven of the area and home to several beaches, with lifeguards on duty and plenty of amenities like bathrooms, picnic areas, boat launches, and rental gear, so it's easy to get stuck here on a beautiful summer day. There are three miles of shoreline and 197 acres of shallow waterways great for swimming, paddling, or canoeing. Castaic Lagoon is also the location of Cali Splash aquapark.

Cali Splash Park is an inflatable water park found right on the lower lake of Castaic Lake. It is open on weekends from Memorial Day through June 14, 2026, after which it is open Wednesday through Sundays through early September. This is the largest inflatable water park in Southern California, full of trampolines, climbing towers, balance bridges, and slides totaling more than 45 obstacles, all on an interconnected floating island in the lake. It is a dream come true for kiddos during summer break, and rivals the lazy river found at this water park.

Sessions are available to book every two hours with a two-hour duration. Visitors can also book a full day or purchase a season pass. Kids age 9 and older may participate on their own, but those between ages 4 and 8 must be accompanied by an adult. Booking in advance is highly recommended, especially on weekends. To stay safe in the water, be sure to check with the California Department of Water Resources website for algae blooms before visiting. They have been known to be common here, and swimming in an algae bloom can be toxic. 

Visitors speak highly of the splash park online. "[Cali Splash Park] exceeded my expectations with its thrilling attractions, pristine facilities, top-notch safety measures, friendly staff, and inclusive fun for all," Ksenia Vedeshenkova wrote in a Google Review. "It's the perfect destination for an unforgettable day of adventure." 

Outside of the water, visitors will find 11,200 acres of park surrounding the lake with plenty of activities to indulge in. There are more than 7 miles of hiking trails, equestrian trails, bird walks, playgrounds, and rental group picnic areas that can host up to 600 people. 

Castaic Lake is located off Interstate 5 at Hughes Lake Road, 41 miles northeast of downtown Los Angeles. For those flying in, LAX will be the nearest airport. The recreation area is open sunrise to sunset, the lake is closed Mondays and Tuesdays, and the inflatable water park and swimming area are open Memorial Day to Labor Day. Aim for a Wednesday or Thursday to avoid the weekend crowds and experience a more serene lakeside feel — which is great for fishing too! Don't have your own gear? No problem. Boat rentals, including 1 or 2 person kayaks and paddleboards, are available, and you can purchase fishing gear at the tackle bait shop on Upper Lake. Many record-setting fish have been caught here, so cast your line out!

Entrance fees are $15 per vehicle, boats cost an additional $13, non-motorized boats are $9, and the area only takes cash or credit cards (bills over $20 will not be accepted). Annual passes to the area can be purchased for those looking to enjoy the fun all season long, and it should be noted that this area does not accept the annual state parks pass of California. 

If you're looking to stay for a few days, the campground at the lake has tent and RV camping each for $31 a day per site. Castaic Lake is yet another coveted California lake with endless outdoor fun.