Medicine Lake is located within Jasper National Park, Alberta, Canada. It is located approximately 20 km (12 mi) southeast of the townsite of Jasper, Alberta. Medicine Lake is approximately 7 km (4.3 mi) long and is a relatively shallow lake. The lake is part of the Maligne Valley watershed which is mainly glacial fed.
Medicine Lake is a geologic anomaly in the sense that it is not actually a lake but rather an area in which the Maligne River (flowing from Maligne Lake into the Athabasca River) backs up and suddenly disappears underground. During the summer months during intensified meltwater runoff the lake (which during the winter months is a meandering frozen river) fills to levels which fluctuate over time and with the runoff events. Much like a bathtub that is filled too fast for it to drain, it becomes laden with water (lake) until it can slowly drain as the tap flow (runoff) is reduced (river). The underground system is extensive and during the 1970s researchers used a biodegradable dye to determine the underground river's extent. The dye showed up in many of the lakes and rivers in the area to the point where it became clear that the underground system was one of the most extensive in the world.