“We will not laugh at the wind, no, no. For it blows the rain for our crops. We will not point with our finger at the sun, no, no. The wrath of the sun is as death. Sing sweetly sisters and let the rain put out the sacred fire.”
THREE TALES OF MYTHOLOGICAL RIVER BEASTS
Kouteign Koorou (Master of the water) 
This serpent lived in the swamps and reeds near the rivers. The San captured it, by weaving enclosures of reeds and poles, so strongly interwoven and bound that the creature could in no way break through. When it could not get out, its’ rages were extreme. It would lash the waters around into such clouds of spray that rainbows appeared as if crowning it. The San also say, that the Fish River Canyon in Namibia, owes its twists and convolutions to the violent rage of this ‘Master of the Water’. Desperate to escape the hunters who pursued it, the monster retreated into the desert, gouging deep scars in the land.
The Inkanyamba 
The legendary water monster of the pools, below Howick Falls. This creature has a horse-like head and a long serpentine body. When looking for a mate, an Inkanyamba will fly into the clouds. When angry, they can create storms, therefore floods. Tribal sacrifices are said to keep the river snake from becoming angry and punishing their villages. In the earlier days, many Zulu people and settlers were washed away while trying to cross the uMngeni River and they were washed down the Falls. That is why it has a sinister reputation. There are also, two species of giant eel, which live in the vicinity. These may be the source.
The Zambezi River-god of the BaTonga People who live in the Zambezi Valley. Nyaminyami is said to reside in the Zambezi River and control the life in and on the river. A hydro-electric scheme was proposed, called the Kariba Dam Project in the 1940s. Many BaTonga were resettled, some resettlements were a disaster. The name Kariba comes from the word Kariva, meaning trap, which refers to a rock jutting out from the gorge where the dam wall was to be built. It was believed by the BaTonga, to be the home of the river-god and that anyone who ventured near the rock was dragged down to spend eternity under the water. In 1957, when the dam was on its way to completion, Nyaminyami struck. The worst floods ever known!! The next season, there were even worse floods. But the great Kariba Dam was finally finished and the mighty Zambezi River controlled. The BaTonga say that Nyaminyami and his wife were separated by the wall across the river and the frequent earth tremors felt in the area since the wall was built are caused by the spirit trying to reach his wife, and that one day he will destroy the dam.
 Miller, P. 1979. Myths and Legends of Southern Africa. T.V. Bulpin. Cape Town
 http://en.wikipedia.org/wiki /The _legend_of_Nyaminyami