Whether its builder is a beaver or a person, a dam is always used for the same purpose: to manage, direct and prevent water flow. Within that definition, there are many different types of dams, from mammoth hydroelectric generators—which produce 20 percent of the worlds' electricity energy and 88 percent of all renewable electricity—to the small sand dams of Kenya that are designed to store water for the dry season. There an estimated 845,000 dams in the world; here are our picks for the 18 strangest.

View Gallery 18 Photos