Lake Tanganyika holds roughly 16 percent of the world's available fresh water, and most of it is lifeless. Below about 200 metres the lake carries no oxygen at all — it is too deep and too warm ever to turn over — so everything alive is pressed into a thin sunlit skin above an abyss that falls to 1,470 metres, a depth beaten only by Baikal. That skin is crowded: some 250 cichlid species live here, about 98 percent of them found in no other water on earth. The lake fills a rift-valley crack 673 kilometres long, which makes it the longest freshwater lake in the world, and it has been filling for 9 to 12 million years. Burundi holds the northern tip, and Bujumbura sits right on the shoreline, looking west across the water at the Mitumba mountains of the Democratic Republic of Congo.
Saga Beach is the strip of pale sand just north of the city, and it is where Bujumbura comes to swim. The water is warm every month of the year, and it runs turquoise over the sand bar before dropping away into blue. Thatched bars stand back from the waterline, hand-paddled wooden canoes work the shallows at dawn, and hippos and Nile crocodiles hold the Rusizi delta a few kilometres north, which is why nobody swims there. Come back after dark on a moonless night and the lake fills with lights, as the ndagala fleet hangs lamps over the water to draw the sardines up. The shore itself is shrinking: since 2019 the lake has risen roughly two metres, swallowing beach plots and lakeside roads and displacing tens of thousands of people along this coast.