Rafferty Dam () is at the south-eastern corner of the lake, about upstream from Estevan. It was built in conjunction with the
Grant Devine Dam (formally known as
Alameda Dam), which was built further downstream on
Moose Mountain Creek. Both dams are operated by the
Saskatchewan Water Security Agency. The dam and reservoir provide flood control along the Souris River, irrigation, and recreation. The height of the top of the dam is above sea level. The maximum height available for flood control is . The normal full supply level is and the normal
drawdown level is . The maximum draw down is above sea level. At full supply, the reservoir covers an area of . Two additional dams were built to contain the reservoir: The high Rafferty R3-2 Closure Dam () and the high Rafferty R4-1 Closure Dam ().
Highway 606 crosses R3-2 and R4-1 is at Mainprize Regional Park. A long spillway connects the
Boundary Dam Reservoir to McDonald Lake, allowing excess water to flow into McDonald Lake. The flow can also be reversed if necessary. In 2025, $15 million was spent in upgrades at the dam. The upgrades included $10 on repairs to the underdrainage system on the dam's spillway, $2.5 million in upgrades to the control structure at the diversion channel, and another $2.5 million in upgrades to the long Rafferty Road. Rafferty road runs along the top of the dam and connects
Highways 18 and
39. == Mainprize Regional Park ==