Lake Tanganyika is an African Great Lake. It is estimated to be the second or third largest freshwater lake in the world by volume, and the second deepest, after Lake Baikal in Siberia. It is situated in the Great Rift Valley. Geologists led by Brown University have determined the east African rift lake has experienced unprecedented warming during the last century, and its surface waters are the warmest on record. That finding is important, the scientists write in the journal Nature Geoscience, because the warm surface waters likely will affect fish stocks upon which millions of people in the region depend.