Lake Kivu fills part of the Rift between Rwanda and the Democratic Republic of the Congo, and it is one of the few big African lakes you can swim in without thinking about it. There are no crocodiles, no hippos and no bilharzia, and the water stays warm all year. At Rubavu you wade straight in off palm-lined sand, with banana-green hills folding down to the shore behind you. The lake owes its shape to the volcanoes at its northern end. It used to drain north towards the Nile, until eruptions from the Virunga range built a barrier of lava across the outlet. Cut off, Kivu rose until it found another way out to the south, and its water has been running the other way ever since, down to the Congo.
The fishing happens at night. After dusk the sambaza crews row out in canoes lashed together in threes and hang lamps over the side to draw the small silver fish up out of the dark. They sing call and response from boat to boat until the catch is in. By day wooden boats and launches cross to the forested islets, some of them ringed with coffee terraces. The track up the Rubona headland gives you the wide version: canoes strung across the water, the town's roofs below, green ridgelines running off towards the Congo shore. The volcanoes left something else as well. Gas seeps into the lake from below and stays dissolved in the deep water, held down by the weight above it, and only two other lakes anywhere are known to hold gas this way. An upheaval could release it all at once, which is what nobody wants. So it is being spent instead. A barge anchored offshore draws water up from about three hundred metres down, the pressure drops, the methane bubbles free, and it goes ashore by pipe to run generators. Every batch taken out leaves the lake a little safer.