Riou Lake,[1] at 16,378.4 hectares (40,472 acres)[2] in size, is a large glacial lake along the course of Riou River[3] in the far northern part of the Canadian province of Saskatchewan.

Stony Rapids, a "two-hour ATV ride"[4] to the east, is the closest community.

The Riou River exits Riou Lake at the western end and flows west into Engler and Richards Lakes.

Lake Athabasca is within the Mackenzie River drainage basin.

[6][7] Fish commonly found in Riou Lake include burbot, cisco, lake trout, lake whitefish, longnose sucker, northern pike, round whitefish, walleye, and white sucker.