In the final episode of the TV series Joanna Lumley’s Nile, Joanna Lumley stretches out next to the muddy dribble that is apparently the furthest source of the White Nile, deep in the mountains of Rwanda, and muses on the fact that this unimpressive wet patch gives rise to such a mighty river. Indeed, it is surprising. Determining the ‘source’ of a river is, it turns out, not a simple matter. There may be many plausible contenders. You can argue that it is the joining together and accumulation of the water from a number of tributaries that constitutes the ‘source’, not any one of them in particular. This issue gave pause even to Victorian explorers, not usually prone to doubts. ‘What should be called the source of a river?’ Henry Morton Stanley asked. ‘A lake which receives the insignificant rivers flowing into it and discharges all by one great outlet, or the tributaries which the lake collects?’ Stanley favoured the former theory, pointing out that otherwise it would be difficult to know where to stop – perhaps with clouds, and the vapours that composed them?

LRB 8 March 2012 | PDF Download