The Maligne River ('maligne' is french for 'malignant' due to the difficulty of crossing) has carved itself the deepest slot canyon in the Canadian Rockies.
Flowing out of Medicine Lake, the Maligne River flows about 15 kilometers upstream as a full size river, but very quickly disappears into seeps in the ground and completely vanishes from the surface not far from the lake for most of the year. The smaller streams that feed the valley below that point rebuild the river by the time it reaches the top of the canyon. As the river drops down into the canyon it intersects the bedrock layers where the underground waters flow. Numerous large underground streams join and greatly increase the flow.