Boundary Dam Reservoir is a man-made lake situated in the southeast corner of Saskatchewan, Canada, approximately 5.5 kilometres upstream from the city of Estevan in the Rural Municipality of Estevan No. 5. The reservoir was created in 1957 when Boundary Dam was constructed on Long Creek, primarily to supply water to the Boundary Dam Power Station and the city of Estevan. Covering approximately 1,415 acres with roughly 22.65 miles of shoreline, the reservoir sits at a full supply level of 560 metres (1,840 feet) above sea level, with the dam crest reaching 563.88 metres. The reservoir's capacity at full supply is 61,480 dam³, with an additional 16,755 dam³ of flood control storage available below the maximum drawdown level of 557.8 metres. Long Creek serves as the primary inflow and outflow, and a 10-kilometre diversion channel connects the reservoir to McDonald Lake, allowing excess water to move in either direction between the two water bodies. The reservoir falls within the Red River drainage basin and is located just off Highway 47, making it readily accessible from Estevan. Woodlawn Regional Park occupies a section of the shoreline and offers a full-service campground, beach, and boat launch facilities. Two residential subdivisions — Sunset Bay and Lakewood — are also situated along the lake's shores.