Located on the east side of the park, Going-to-the-Sun Road parallels the lake along its north shore. At an altitude of , Saint Mary Lake's waters are colder and lie almost higher in altitude than Lake McDonald, the largest lake in the park, which is located on the west side of the Continental Divide. Here, the great plains end and the Rocky Mountains begin in an abrupt altitude change, with Little Chief Mountain posing a formidable southern flank above the west end of the lake.