Montreal Lakes's catchment includes the northern slopes of the Waskesiu Hills[4] and the southern and eastern slopes of the Thunder Hills.[5] Waskasiu River is the primary inflow. It enters the lake at its south-western shore and its drainage basin includes the aforementioned Waskesiu Hills, Waskesiu Lake, and Kingsmere Lake. Also on the western shore is the Weyakwin River, which flows from Weyakwin Lake, and MacLennan River, which flows from the south side of the Thunder Hills. One of MacLennan River's tributaries, the Crean River, flows in from Crean Lake. At the southern tip of the lake, Bittern River flows in from Bittern Lake. Montreal River flows out of Montreal Lake at O'Connor Bay[6] at the north end. Montreal River heads northward and flows into Lac la Ronge.
^"Wasesiu Upland". The Encyclopedia of Saskatchewan. University of Saskatchewan. Archived from the original on 25 July 2021. Retrieved 8 September 2022.
^"Thunder Hills". Canadian Geographical Names Database. Government of Canada. Retrieved 8 September 2022.
^"O'Connor Bay". Canadian Geographical Names Database. Government of Canada. Retrieved 9 September 2022.