Lake Manitou is the largest lake on Manitoulin Island in Ontario, Canada. It is the largest lake on a lake island in the world. Since Manitoulin Island itself is in Lake Huron, one of the Great Lakes, Manitou qualifies as the largest "lake in a lake". Lake Manitou has an area of about 104 square kilometres (40 sq mi). It is drained by the Manitou River. There are also a number of small islands in Lake Manitou, making them islands in a lake on an island in another lake.
Manitoulin Island location in the Great Lakes