Boundary Dam Reservoir is a man-made lake in the south-east corner of the Canadian province of Saskatchewan.

There is a 10-kilometre (6.2 mi) long diversion channel that goes to McDonald Lake that can take excess water in either direction.

The reservoir, though, is not intended for flood control as its value is in the water it supplies to the power station.

A three year project, that ran from 2017 to 2020, changed the city of Estevan's water supply from Boundary Reservoir to McDonald Lake.

Boundary Dam Reservoir is the only lake in Saskatchewan that has a large area that does not freeze over in the winter due to warm water being returned to the lake from the Boundary Dam Power Station.