Lake Dennison Recreation Area is a 121-acre Massachusetts state park in the town of Winchendon, run by the Department of Conservation and Recreation (DCR) out of the Otter River State Forest office. The land belongs to the U.S. Army Corps of Engineers as part of the Birch Hill Dam flood control project on the Millers River watershed, and the state manages it for recreation under a long-standing arrangement. The swimming is in Lake Dennison itself, a lake of roughly 82 to 85 acres with a shoreline that is almost entirely wooded and undeveloped. The day-use beach sits at the south end of the lake, a short distance from the main campground.

The park is on Route 202 (Baldwinville State Road) north of Baldwinville and about four miles south of downtown Winchendon. From Route 2, take Route 202 north for roughly six miles. The campground address is 219 Baldwinville State Road, Winchendon, but that gate leads to the camping loops. Day visitors use the separate day-use entrance, which leads to a parking lot just behind the beach and picnic grove, so the walk to the sand is short.

The beach is a strip of sand on the lake's southern shore, and the bottom is sandy. The water is clean but tea-colored from natural tannins, which limits how far down you can see, and the lake averages about 8 to 9 feet deep with the deepest spots near 18 feet, so the bottom drops away once you leave the shallows. It is a shallow, sheltered lake that warms up well by midsummer, and there is no current to speak of. DCR lists beach hours of 10 a.m. to 8 p.m. daily from late May to early September. Lifeguard coverage is not stated on the state's park page, so check the posted signs at the beach and assume you are swimming on your own outside guarded hours. Beach wheelchairs are available.

The charge here is a state parking fee per car during the summer season. In 2026 DCR charges $8 per vehicle with Massachusetts plates and $30 for vehicles with out-of-state plates, collected 9 a.m. to 5:30 p.m. daily from May 23 through September 7. Residency is decided by the license plate. DCR's annual state parks parking pass and lifetime senior pass cover the fee.

Dogs are allowed in the park but not on the beach, and alcohol is prohibited throughout. Natural lakes have sudden drop-offs, underwater branches and poor visibility, and the dark water here makes a struggling swimmer hard to spot, so keep children within reach. Boats and paddlers use the lake as well. Only non-motorized boats and small outboards (10 horsepower or less) are allowed, and the car-top boat ramp is on the west shore north of the beach. DCR posts trail closures on its park page.

The day-use area has a pavilion, picnic tables, grills and restrooms. The campground has 150 sites, several of them right on the water, plus a small beach of its own for campers in the North Camping Area. In 2026 sites cost $17 a night for Massachusetts residents and $54 for non-residents. More than 50 miles of trails link the park with the Birch Hill Wildlife Management Area for hiking, mountain biking and horseback riding, and Otter River State Forest is about a mile and a half to the south. Anglers fish the lake from shore and from canoes and kayaks.