Mokele-mbembe

Mokèlé-mbèmbé, meaning "one who stops the flow of rivers" in the Lingala language is a legendary water-dwelling creature of Congo River basin folklore, sometimes described as living creature, sometimes as a spirit, and loosely analogous to the Loch Ness Monster in Western culture. It is claimed to be a sauropod by some cryptozoologists.
Expeditions mounted in the hope of finding evidence of the Mokèlé-mbèmbé have failed, and the subject has been covered in a number of books and by a number of television documentaries.