Lake Alvin Recreation Area is a 59-acre state recreation area run by South Dakota Game, Fish and Parks in Lincoln County, about 13 miles southeast of Sioux Falls and a few miles east of Harrisburg. It sits on the shore of Lake Alvin, a 105-acre reservoir formed when a dam was built across the lower end of Ninemile Creek. The dam was finished in August 1954 and the lake filled by 1957. It takes its name from Alvin Dempewolf, a Harrisburg soldier who died overseas in World War I. GFP describes the park as small but busy, and the beach is the main reason most people come.

From Harrisburg, head about 4 miles east and then 1 mile north off County Road 135. The park address is 27225 480th Avenue, Harrisburg. It is a day-use park only, with no campground, and it is open year-round. The swim beach is on the north shore of the lake, along the park road, with parking, restrooms and a picnic shelter close by, so it is a short walk from the car to the water.

The designated swim beach is a short stretch of shoreline facing south across the lake, with open water out front and wooded bluffs on the far side. The lake is a no-wake zone where boats may not go faster than 5 mph, so the swimming area stays calm even on busy weekends. This is a small reservoir fed by a creek that drains farm country, so expect lake water rather than clear water, and expect it to cloud up after a hard rain. GFP's park page does not list lifeguard service, so watch your own group, especially kids.

Swimming itself costs nothing extra, but every vehicle needs a South Dakota state park entrance license. The daily license is $10 for residents and $15 for nonresidents, and the annual license is $40 for residents and $60 for nonresidents. You can buy one online or at the self-serve kiosk at the park entrance. Between October 1 and April 30, showers, flush toilets and other water systems may be shut off, though the vault toilets stay open.

Check conditions before you go. GFP tests the beach water, and the beach has been closed several times after heavy rain washed bacteria into the lake, including in 2009, 2013, 2014, 2020 and 2021. Each time it reopened once follow-up samples came back clean. The beach and boat ramps were also closed from July 2024 while the lake was drawn down more than 10 feet to replace the spillway, which flooding damaged in 2019. That work added two picnic shelters and a vault toilet near the beach, and by June 2026 the lake was back to full pool. Aquatic plants have since spread along parts of the shoreline, and some neighbors say a few edges have turned marshy, so the designated beach is the place to get in. If you have doubts about the current status, call the park at 605-987-2263.

Outside the water, the park has a boat ramp, a fishing pier, shore fishing access, group picnic shelters, picnic tables and a playground. Anglers go after walleye, northern pike, crappie, perch, sunfish, catfish and bullheads, and the no-wake rule makes it a good lake for canoes, kayaks and paddleboards. There is no camping here, but Newton Hills State Park, whose office also handles Lake Alvin, is a short drive south and has a campground if you want to stay overnight.