A geological rarity, Medicine Lake is perhaps best described as an intermittent lake with a porous bottom that functions rather like a bathtub without a plug. In summer, when meltwater runoff is high, the lake fills more quickly than it can drain away, and the body of water becomes deep and expansive. In winter, as the runoff slows, the water empties, causing the lake to shrink to the size of a small stream.
What bewildered indigenous peoples and other early visitors was the apparent lack of any water outlet. In fact, the water flows out of the lake via a series of small holes on its floor before passing into a complex underground cave system. The river then re-emerges 16km downstream near Maligne Canyon. In the 1950s a ferry service across the lake was briefly attempted, but efforts to plug the holes with sandbags, mattresses and bundles of magazines all proved futile.
