Today I went swimming in Lake Kivu, the sixth largest lake in Africa. On one side is Rwanda, on the other Congo. The water was a perfect temperature - refreshing but not too cold. And just enough waves to bounce you around a bit. Supposedly, there is methane gas under the lake, which at anytime could burst forth and wipe out the population of Goma. But then, you could get hit by a Land Cruiser crossing the street.
Later in the day, at dinner, I learned the lake was a dumping ground for bodies during the Rwandan genocide in 1994. More recently, contaminated lake water has caused cholera outbreaks in Goma.