Larken, Paul Metcalf "An Account of the Zande," Sudan Notes and Records, Vol. 9 (1926)

The existence of various monsters, which may reservedly be called mythical, is believed in. It is noticeable that they are all said to live in rivers, and none on dry land.
The ndutu is bigger than a house. Its skin is covered with a growth of grass and water weeds. Nobody of the present day has ever seen one. They live in some of the smaller streams, but mostly in the big rivers like the Sue. They are so huge that they have stopped the course of that river ere now.
Moma ime, or the water leopard, are said to live in deep pools of large rivers, and big fissures in the banks have often been pointed out as being their homes.
Wanga, a kind of lizard with a smooth skin like a fish, inhabits only the Congo or the Nile. It has breasts.
Ngambue, a big snake, its skin covered with a substance like flour, and possessing a beard, may live in all waters. The well in Yambio was thought to harbour one. Its bite is poisonous.
There is also a beast, of unknown name, with a prehensile limb like an elephant's trunk that lives in rivers, and seizes people with its tentacle. They are not in the Sue but only in the Were River in the Congo. They do not eat the bodies of their victims, but merely suck their blood. It was reported to an English Missionary that a bloodless corpse had been found in a stream in the Congo, which had been sucked dry by this creature.