The swimming beach at Lake Kegonsa State Park is the Wisconsin DNR's designated swim area on Lake Kegonsa, the southernmost and third largest of the four Yahara River lakes in Dane County. The park covers about 342 acres on the lake's northeast shore, roughly four miles north of downtown Stoughton and southeast of Madison. Lake Kegonsa itself is a glacial lake of about 3,200 acres with a maximum depth a little over 30 feet, and the beach sits a short walk up the shore from the Yahara River outlet and the La Follette dam.

The park entrance is at 2405 Door Creek Road in the Town of Pleasant Springs, close to Interstate 39/90. Follow the park road past the office toward the lake; the beach has its own parking lots just behind the sand, with a bathhouse and restrooms a few steps from the water. A paved half-mile Lakeshore Trail runs along the shoreline from the beach to the boat landing, and a short wetland boardwalk near the beach ends at a wildlife viewing platform where geese and ducks gather.

The swim area is a short strip of beach on the open lake, and the DNR does not publish depths for it, so check the bottom as you wade out. The DNR does not post lifeguards here, so everyone swims at their own risk and children need an adult watching them. Swimming is a summer activity in practice: the lake is ice-covered most winters and stays cold well into June, then warms through July and August. Pets are not allowed on the swim beach. Dog owners can use the separate Pet Swim Area a little to the east along the same shore, with dogs on a leash 8 feet or shorter.

Lake Kegonsa State Park is open year-round from 6 a.m. to 11 p.m. Swimming is not free here, because every motor vehicle stopping in a Wisconsin state park needs a vehicle admission pass. A daily pass costs $13 for a car with Wisconsin plates, $3 for Wisconsin residents age 65 and older, and $16 for out-of-state plates. A 12-month pass is $28 for Wisconsin plates and $50 for out-of-state plates. Passes are sold online and at the park, and visitors who skip paying face an extra $5 charge or a citation.

The main hazard is water quality. Lake Kegonsa sits downstream of Madison and its farm watershed, and blue-green algae (cyanobacteria) blooms can show up any time in summer. The DNR posts signs at the beach when it closes the swim area, and Wikipedia's article on the park notes the beach may be closed during blooms. Stay out of water that looks like green paint, pea soup or scum, rinse off after swimming, and keep dogs out of bloom water. Boats, jet skis and sailboats share the lake, so stay inside the swim area.

The rest of the park makes a full day out of a beach visit. There are more than five miles of trails, including the 1.2-mile White Oak Nature Trail through an 80-acre oak woods with effigy mounds, plus the Prairie Trail through restored prairie. There are reservable picnic shelters, a boat launch with accessible boarding piers, an accessible fishing pier and a family campground with 96 sites that is open from May through October. Walleye, northern pike and panfish draw anglers year-round, and kayaks, including an adaptive tandem kayak, can be rented in season.