evidence: Tensions about rights to the lake that lies between Tanzania and Malawi have been brought to boiling point yet again. Known to Tanzanians as Lake Nyasa but as Lake Malawi to those across the border, the lake is at the centre of a boundary dispute that has simmered for decades. In the latest exchanges, the foreign minister of Malawi has threatened to escalate the dispute to the International Court of Justice in The Hague. [...] The Malawi-Tanzania case therefore presents two apparently irreconcilable positions on the delimitation of Africa’s third largest lake. Unique to this dispute is the way it turns on the question of treaty law versus customary international law governing the delimitation of fluvial bodies. [...] There is now no doubt at all about the boundary. We know that not a drop of water of the Lake Nyasa belongs to Tanganyika…