The Lukuga River is a tributary of the Lualaba River in the Democratic Republic of the Congo (DRC) that drains Lake Tanganyika. It is unusual in that its flow varies not just seasonally but also due to longer term climate fluctuations. Location The Lukuga runs along the northern edge of the Katanga Plateau. The river leaves Lake Tanganyika at Kalemie and flows through a gap in the highlands westward through the Tanganyika District to join the Lualaba between Kabalo and Kongolo. Typically the river accounts for 18% of water loss from the lake, with the rest being due to evaporation. The Lukuga is heavily mineralized. The proportions of ionic contents where the Lukuga River leaves the lake, with magnesium and potassium more prevalent than calcium and sodium, are caused by the Albertine Rift's hydrothermal inputs, as seen also at the outlets of Lake Kivu and Lake Edward. It seems likely that the present hydrological system was established quite recently when the still-active Virunga volcanoes erupted and blocked the northward flow of water from Lake Kivu into Lake Edward, causing it instead to discharge southward into Lake Tanganyika through the Ruzizi River. Before that, Lake Tanganyika, or separate sub-basins in what is now the lake, may have had no outlet other than evaporation. The Lukuga is of considerable interest to hydrologists, since the volume of water it carries from the lake varies considerably from time to time. The river flow is greatest in May and least in November, corresponding to seasonal fluctuations in the lake level. The river is highly sensitive to longer-term climate variations, such as the Neolithic Subpluvial around 4000 BC. Since 1965 the outflow has tended to increase, although the total outflow of the Congo has been declining. The Lukuga has formed relatively recently, providing a route through which aquatic species of the Congo Basin could colonize Lake Tanganyika. The river is home to hippopotamus and crocodiles. There are low-grade coal deposits along the river's tributaries north of Kalemie and Moluba. Early years The Lukuga in the north, Lake Tanganyika, the Luvua River to the south and the Lualaba form a territory that was once occupied by the Hemba people in the western part and the Tumbwe people in the more mountainous east. Kasangas of the Tumbwe lineage ruled various small states in this region. The lower Lukuga and the Lualaba were natural lines of communication, and the