Lake Victoria is one of the African Great Lakes. With a surface area of approximately , Lake Victoria is Africa's largest lake by area, the world's largest tropical lake, and the world's second-largest fresh water lake by surface area after Lake Superior in North America. In terms of volume, Lake Victoria is the world's ninth-largest continental lake, containing about of water. Lake Victoria occupies a shallow depression in Africa. The lake has an average depth of and a maximum depth of . Its catchment area covers . The lake has a shoreline of when digitized at the 1:25,000 level, with islands constituting 3.7% of this length. The lake's area is divided among three countries: Kenya occupies 6% (), Uganda 45% (), and Tanzania 49% (). Though having multiple local language names (; ; ; also Ukerewe), the lake was renamed after Queen Victoria by the explorer John Hanning Speke, the first Briton to document it in 1858, while on an expedition with Richard Francis Burton. The lake is home to many species of fish which live nowhere else, especially cichlids. Invasive fish, such as the Nile perch, have driven many endemic species to extinction. Geology Geologically, Lake Victoria is relatively young at about 400,000 years old. It was formed when westward-flowing rivers were dammed by an upthrown crustal block. During the Miocene era, what is now the catchment area of the lake was on the western side of an uplifted area that functioned as a continental divide, with streams on the western side flowing into the Congo River basin and streams on the eastern side flowing to the Indian Ocean. As the East African Rift System formed, the eastern wall of the Albertine Rift (or Western Rift) rose, gradually reversing the drainage towards what is now Lake Victoria. The opening of the main East African Rift and the Albertine Rift downwarped the area between them as the rift walls rose, creating the current Lake Victoria basin. During its geological history, Lake Victoria went through changes ranging from its present shallow depression, through to what may have been a series of much smaller lakes. Geological cores taken from its bottom show Lake Victoria has dried up completely at least three times since it formed. These drying cycles are probably related to past ice ages, which were times when precipitation declined globally. Lake Victoria last dried out about 17,300 years ago, and