Lake Tanganyika is the world’s second-deepest lake and is famous for its extraordinary diversity of endemic cichlid fishes.
The lake lies in the East African Rift between Tanzania, the Democratic Republic of the Congo, Burundi, and Zambia. Its deepest point is about 1,470 metres, surpassed only by Russia’s Lake Baikal. Tanganyika is also one of the world’s oldest lakes, giving species millions of years to evolve in relative isolation.
More than 200 fish species are found in the lake, and many are endemic, meaning they occur naturally nowhere else. Its cichlids occupy remarkably specialized ecological niches, including rock-dwelling, shell-dwelling, algae-grazing, and scale-eating species.
“Lake Nyasa” is an alternate name for Lake Malawi, so it is not a separate answer from Lake Malawi. Lake Victoria is Africa’s largest lake by surface area, while Lake Tanganyika is the deeper and older rift-lake habitat highlighted by this question.