Barns, Thomas Alexander & Johnston, Hary H. (1922) The Wonderland of the Eastern Congo, pp. 190-192

 ... the natives in many parts of Central Africa believe in the existence of a gigantic water animal which has been described to me by the Buanga natives inhabiting the swamps of the south of Lake Bangweulu, as a water rhinoceros; they had even a name for it, which was chimpelwi, and described it as able to kill a hippopotamus with which it was in the habit of fighting; the bones of one of these animals, they averred, were to be found in the swamps.

An authenticated case of a white man having seen such an animal was told me by the man himself, an acquaintance of mine named Defries [sic]. It is, of course, necessary to state he is an extremely abstemious man, besides being a good sportsman, a trained naturalist, and for a considerable period rubber conservator for North-western Rhodesia. When carrying out his duties in the latter capacity he had reason to pass by a small lake between Lakes Chaa and Kapopo on the upper Kafue River. This lake or rather lakelet is so deep as to be unfathomable, and has moreover no visible outlet.

Defries put up his tent near by and towards evening whilst strolling to the water's edge with his rifle, he was astonished to see a massive form lying or floating on the water. Now, Defries was a very old resident in Central Africa and knew a hippo as you, dear reader or I, know a bull in a field, perhaps better, and he emphatically states it was not a hippo. He describes it as a long, dark floating body, at which he fired and which he hit, being not more than sixty yards from it, whereupon the animal disappeared amidst a considerable commotion in the water. He never saw the beast again although he waited the whole of the next day on the off-chance, and moreover he examined the complete circle of the lake for spoor, but could find no large tracks of any description either leading to or from the water. He reported the matter to Sir Robert Codrington, who was then the Administrator of Northern Rhodesia, and wrote a report to some museum authorities and there the matter dropped.

...

Native tradition, legend or belief, call it what you will, bears out this theory. You find it always in lacustrine districts and the report has come to me from many places–from the Albert Nile, from the Highlands of the Great Craters west of Kilimanjaro, from Lake Leopold II, and from Lake Bangweulu. My own actual experiences concerning such an animal confine themselves to the accounts given me by the Buanga natives of Bangweulu, and a large-sized native drawing of a beast resembling in all essentials a brontosaurus, which I found on a hut in the Ituri forest. I will conclude this diversion by remarking that we know such animals did, at one time, exist in Africa, for the largest fossil specimen ever discovered–which is known as the gigantosaurus and over one hundred feet long–came from German East. It is, however, improbable that one of these great saurians still exists, although possible that some large water animal may yet be undiscovered, as we have seen from Mr. Defries' experience.