Lake Victoria

Lake Victoria ranks among the African Great Lakes. Spanning roughly 59,947 square kilometers (23,146 square miles), it holds the title of Africa’s largest lake by surface area, the biggest tropical lake on Earth, and the second-largest freshwater lake by surface area globally—trailing only Lake Superior in North America. By volume, it is the ninth-largest continental lake, holding about 2,424 cubic kilometers of water. Its territory is split among three nations: Tanzania claims 49 percent (33,700 square kilometers), Uganda 45 percent (31,000 square kilometers), and Kenya 6 percent (4,100 square kilometers).

The lake sits in a shallow depression, with an average depth of 40 meters (130 feet) and a maximum depth of 80 to 81 meters (262–266 feet). Its catchment area covers 169,858 square kilometers (65,583 square miles), and its shoreline, when mapped at a 1:25,000 scale, stretches 7,142 kilometers (4,438 miles), with islands making up 3.7 percent of that length.

Many fish species found nowhere else inhabit the lake, particularly cichlids. However, invasive species like the Nile perch have driven numerous endemic fish to extinction.

Known by several local names—including Ukerewe in Swahili, Nam Lolwe in Dholuo, Nnalubaale in Luganda, and Nyanza in Kinyarwanda—the lake was renamed after Queen Victoria by British explorer John Hanning Speke, who first documented it for Europeans in 1858 during an expedition with Richard Francis Burton.

Geologically, Lake Victoria is relatively young, about 400,000 years old. According to photojournalist John Reader, it formed when westward-flowing rivers were dammed after a fractured block of the Earth’s crust tilted along the Great Rift Valley, raising its western edge. During the Miocene epoch, the area that is now the lake’s catchment lay west of an uplifted continental divide, with streams flowing west into the Congo River basin and east toward the Indian Ocean. As the East African Rift System developed, the eastern wall of the Albertine Rift rose, reversing drainage toward what is now Lake Victoria. Later, the opening of the main East African Rift and the Albertine Rift downwarped the land between them, creating the current basin. Over time, the lake has shifted from its present shallow form to possibly a series of smaller lakes. Geological cores reveal it has completely dried up at least three times since forming, likely during past ice ages when global precipitation dropped. It last dried out about 17,300 years ago and refilled 14,700 years ago, at the start of the African humid period.

Hydrologically, Lake Victoria gets 80 percent of its water from direct rainfall. Average annual evaporation ranges from 2.0 to 2.2 meters (6 feet 7 inches to 7 feet 3 inches), nearly double the precipitation in surrounding areas. Rivers and thousands of small streams supply the rest. The Kagera River, entering on the western shore, is the largest inflow. The lake drains solely via the Nile River, which exits near Jinja, Uganda, on the northern shore. In Kenya, major influent rivers include the Sio, Nzoia, Yala, Nyando, Sondu Miriu, Mogusi, and Migori. Because of its outflow, Lake Victoria is the principal source of the Nile’s longest branch, though the most distant source of the Nile Basin is often considered one of the Kagera River’s tributaries, originating in either Rwanda or Burundi. The Nile’s uppermost section is called the Victoria Nile until it reaches Lake Albert; the name White Nile technically applies only after the river crosses into South Sudan.

The lake is eutrophic. Between 1990 and 1991, oxygen levels in the mixed layer were higher than in 1960–1961, with nearly continuous oxygen supersaturation at the surface. However, oxygen in the hypolimnion (the cold, non-circulating layer below the thermocline) was lower and lasted longer, with concentrations below 1 milligram per liter occurring as shallow as 40 meters, compared to a minimum of 50 meters in 1961. These changes align with higher algal biomass and productivity, driven by successive basin fires depositing soot and ash, increased nutrient inflows from rivers, and pollution from growing lakeside settlements.

From 2010 to 2022, the lake’s surface area expanded by 15 percent, flooding nearby communities.

Despite its vast size, the lake is shallow, with a maximum depth of about 80 meters and an average of 40 meters. A 2016 project digitized ten thousand points to produce the first accurate bathymetric map of the lake.