Uniamési

Lake Uniamési or the Uniamesi Sea was the name given by missionaries in the 1840s and 1850s to a huge lake or inland sea they supposed to lie within a region of Central East Africa with the same name.
Three missionaries, confined to the coastal belt, heard of the region of Unyamwezi in the northwest of what is now Tanzania and exaggerated its size to include a large part of the continental interior. They heard of a great lake, and imagined an enormous lake that would be the source of the Benue, Nile, Zambezi and Congo rivers. They drew a map showing a huge "Lake Uniamesi" that was published in 1855. The map spurred the expedition of Burton and Speke to investigate the African Great Lakes region, where they found that lakes Victoria, Tanganyika and Nyasa were separate bodies of water. It was not until 1877 that it was confirmed that these lakes did feed the Nile, Congo and Zambezi, albeit separately.