Lake O' the Dalles Beach is the swimming beach at Interstate Park, the Wisconsin state park on the St. Croix River just south of downtown St. Croix Falls. The Wisconsin Department of Natural Resources manages the park, which opened in 1900 and is the oldest in the state system. The beach sits on the east shore of Lake O' the Dalles, a small lake tucked into a wooded basin below the basalt bluffs of the Dalles of the St. Croix, the gorge that gives the lake its name. A Minnesota park of the same name sits across the river in Taylors Falls, but the lake and its beach are on the Wisconsin side.

The park entrance is on State Highway 35 at the south edge of St. Croix Falls, close to where U.S. Highway 8 crosses the river into Minnesota. Follow the park road to the beach area, where there is a parking lot a short walk from the sand, along with a picnic shelter, a playground and flush toilets. The stone beach house above the shoreline was built by the Civilian Conservation Corps in the 1930s and is still in use. A hiking route, the Lake O' the Dalles Trail, loops around the water from the beach.

The beach itself is a strip of sand at the foot of a grassy lawn. A restoration project around 2019 took out an old retaining wall, roughly doubled the size of the sand area and eased the slope above it. The bottom is sand near shore, but the DNR warns that depth can change abruptly, so wade in carefully, especially with kids. No lifeguards are on duty at any time. The lake is calm water with no current, and only nonmotorized boats are allowed, so swimmers share it with canoes, kayaks and people fishing from shore. There is also an accessible shore fishing station on the lake.

Swimming is not free. Every vehicle in a Wisconsin state park needs an admission pass. Since Aug. 19, 2025, a daily pass costs $13 for a car with Wisconsin plates, $3 for Wisconsin residents 65 and older, and $16 for out-of-state plates. Annual passes run $28 for Wisconsin plates and $50 for out-of-state vehicles. Visitors who use the park without buying a pass first owe an extra $5 and can be cited. The park is open from 6 a.m. to 11 p.m. every day of the year, but the beach area flush toilets and drinking fountains are shut off at the end of September each year.

Stay in the lake. The DNR prohibits swimming in the St. Croix River upstream of the park boat launch, and cliff jumping is banned along the whole river, where fast current runs through the gorge. As of October 2026, the park says several construction projects running through fall 2026 will affect availability of the beach and other facilities, so check the park conditions page before you go.

There is plenty to fill the rest of the day. The park has two campgrounds, the Ice Age Interpretive Center, and trails along the river bluffs to the glacial potholes and overlooks of the Dalles. The Pothole Trail, which drops down among the rock formations at the river's edge, starts a short drive north of the beach.