Take Africa’s largest lake, pull the plug, and watch as millions of tonnes of water sluice through… That plughole is Jinja in Uganda where Lake Victoria’s contents spill out, forming the Nile and some of the world’s most spectacular rapids. Hurtle down a broiling field of spray, being flung from side to side at the mercy of age old currents, and cling on, heart in mouth, as the raft’s nose rides abruptly over a curling crest – and all this with only helmet and paddle for protection.