Reid Lake, also known as Duncairn Reservoir, is a man-made reservoir in southern Saskatchewan, located approximately 39 kilometres southwest of Swift Current in the RM of Webb No. 138. The reservoir was created in 1942 with the construction of the Duncairn Dam along a glacial meltwater channel on Swift Current Creek, originally built to supply water to Swift Current, support irrigation, and regulate downstream creek levels. The lake covers a surface area of 1,430.2 hectares (3,534 acres) with a maximum depth of 10.4 metres (34 feet).

The entire lake falls within the Duncairn Reservoir Migratory Bird Sanctuary, making it a notable destination for wildlife observation while on the water. The Duncairn Dam sits at the northern end of the lake. Swift Current Creek flows both into and out of the reservoir, and when water levels allow, paddlers can extend trips upstream along the creek — a route that has been used for guided kayak tours operating out of the Simmie area.

There are four boat launches around the lake providing water access, including a north boat launch near the dam and at least three launch points on the south end of the lake. At least one of these launches features a dock and is noted for good shore access as well. The lake is accessible via Highways 631 and 343. Cabins are available in the area, including at Carefree Park near Simmie.

Fish species present in the lake include walleye, yellow perch, northern pike, white sucker, and burbot, so paddlers should be aware of fishing activity on the water. The reservoir is managed by the Saskatchewan Water Security Agency.

Kayaking has been offered commercially on Reid Lake, with guided tours and lessons historically available through a local outfitter based near Simmie. The operation has introduced paddlers to both flatwater kayaking on the reservoir and creek paddling on Swift Current Creek, suggesting the lake is well-suited to recreational flatwater paddling.