The shifts are not just seasonal. The rainy season fills the lake; the dry season shrinks it. But the bigger swings run on scales of years and decades, and rainfall alone does not explain them. The lake's maximum depth has been measured at five meters, and at times most of its surface has held less than one meter of water. Salinity has fluctuated along with water level, making Mweru Wantipa both a scientific curiosity and a practical problem for anyone trying to make a living from it. Its position doesn't help either - remote, overshadowed by famous neighbors. Lake Tanganyika sits 25 kilometers to the east, Lake Mweru 40 kilometers west. Both are bigger. Both are easier to reach. Geographers and geologists have spent their attention there, leaving Mweru Wantipa to keep its secrets.

Mweru Wantipa lies in a side arm of the East African Rift, the vast tectonic scar running from the Luapula River up to Lake Tanganyika. Hot springs east of the lake are one of the rift valley's fingerprints. Water flows in from streams off the Mporokoso plateau 32 kilometers to the south, and from hills northeast in the Democratic Republic of the Congo. The drainage, though, is strange. The lake was once thought to drain via the Mofwe dambo and the Kalungwishi River into Lake Mweru. But the Kalungwishi's elevation at the junction is 942 meters while Mweru Wantipa sits at only 932 - so the Kalungwishi actually flows into Mweru Wantipa in the rainy season, not out of it. In 1931 after torrential rain, for once, the flow briefly reversed.

For all its strangeness, the lake is alive. Hippos and crocodiles are abundant. Waterfowl fill the marshes. Mweru Wantipa National Park covers the western shore, the lake surface itself, much of the marshland, and part of the southern shore. On land, though, the wildlife that once roamed here has been heavily reduced. The fishery was once productive and has been depleted in recent decades. Some of the pressure comes from across the northern border: the lake sits only a few kilometers from the DRC, and wars there have sent thousands of refugees across the line into the Kaputa area. Most have been moved to camps at Kawambwa and Mporokoso before repatriation. A peninsula at Kampinda in the southeast closes off a swampy inlet called Chimbwe Pools and a lagoon known as Lake Cheshi.

Kaputa is the main center of population on the lake and the seat of an administrative district in the Northern Province. It is the town the refugees first reach when they cross the border, and the market town for people who live along the lake's northern shore. For a time the principal road to the lake ran from Mporokoso down to its southeast shore, where a ferry crossed at Bulaya. That road has deteriorated. The main highway now comes in from Lake Mweru along the western and northern shores to Kaputa. Standing on those shores you look at water that has refused, for a hundred documented years, to settle on what it wants to be. Lake. Swamp. Dry plain. Sometimes all three in a decade.