Which African lake is the source of the Nile River?

In which country is Lake Onega located? In which country is Lake Khövsgöl located? Which lake is the second-deepest lake in the world? In which country is Lake Poyang located? Which lake is located on the border of Tanzania, Uganda, and Kenya? Which lake is located in the Himalayas and is a sacred site in Hinduism? What is the largest lake in Central America? What is the largest lake in Turkey?