Okavango Delta: Floods of Life

The Okavango river transports freshwater and nutrients thousands of kilometres across the drylands of southern Africa, before spilling into and transforming the Kalahari desert basin. This aerial photograph also captures the smoke of fires burning in the desert Photograph: NASA/Corbis Photograph: NASA/guardian.co.uk A reed frog clings to a water lily. The Okavango delta is a unique natural phenomenon that acts as an oasis of wildlife – from big game such as elephants, lions and buffalo, to 99 species of dragonfly, as well as hundreds of different wildflowers. It is also extremely valuable to humans, not only for hunting and tourism but as a rich provider of food, fuel and building materials Photograph: Frans Lanting/Corbis Photograph: Frans Lanting/guardian.co.uk The threats facing the Okavango include a booming elephant population (pictured here), climate change and wildfires Photograph: Michael Poliza/NGC/Getty Photograph: Michael Poliza/NGC/guardian.co.uk The river drains down in tributaries from the wet highlands of north-east Angola, crossing thousands of square kilometres of pristine wilderness, once known in Angola as terra do fim do mundo , Portuguese for the land at the ends of the earth Photograph: Michael Fay/NGC/Getty Photograph: Michael Fay/NGC/guardian.co.uk It sometimes forms meanders so wide that the water flows across the channel as much as it does downstream Photograph: Frans Lanting/Corbis Photograph: Frans Lanting/guardian.co.uk The water finally spills out into the bottom of the desert basin, flooding it Photograph: Sue Flood/Getty Photograph: Sue Flood/guardian.co.uk Pulses of water from rains upriver – some huge, others smaller – arrive in the "blood system" of wandering channels. Water also seeps out into backwashes of marshland, where it eventually evaporates or drains into the sand below Photograph: Frans Lanting/Corbis Photograph: Frans Lanting/guardian.co.uk A crocodile and a group of lechwe antelope get acquainted on an island just barely above the level of the river. Islands of trees, on old termite mounds or the partially submerged ridges of old channels, act like kidneys, leeching salts out of the water and pumping the freshwater back into the atmosphere Photograph: Bobby Haas/NGC/Getty Photograph: Bobby Haas/NGC/guardian.co.uk Night blooming water lilies ( Nymphaea nouchali ). During its long, slow journey, the river water is also filtered by the Kalahari sands, reeds and papyrus. Much of the delta water is said to be better quality than bottled water Photograph: Frans Lanting/Corbis Photograph: Frans Lanting/guardian.co.uk Nutrients in the soils and plants build up underwater, much like the fat deposits in a body. When the water dries out, they are released from the drying peat and vegetation, as in this aerial view Photograph: Martin Harvey/Getty Photograph: Martin Harvey/guardian.co.uk A water hole. Each year floodwaters bring life, but then recede so that nutrients are returned to the soil, ready for further bouts of production in the years ahead Photograph: Frans Lanting/Corbis Photograph: Frans Lanting/guardian.co.uk To cope with the changing water distribution, plants and animals – such as these African buffalo ( Syncerus caffer ) – have learned to move with it. Alternatively, some life simply waits, for years or even decades, in the form of eggs, seeds, spores, pupae or slumbering adults, for the water to return Photograph: Beverly Joubert/Getty Photograph: Beverly Joubert/guardian.co.uk A crocodile looks nonplussed at his dragonfly visitor. Relatively few species actually live in the water, with most thriving instead in the ever-changing patchwork of nutrients of the seasonal swamps and occasional floodplains Photograph: Beverly Joubert/NGC/Getty Photograph: Beverly Joubert/NGC/guardian.co.uk A butterfly spreads its wings on a wildflower. On the fertile drier plains, plants thrive: acacia and mopane woodlands; shrubs perhaps stunted by fire, frost, browsing elephants or the soil; and 1,300 flowering plants, including grasses, sedges, asters, daisies, beans and peas Photograph: Beverly Joubert/NGC/Getty Photograph: Beverly Joubert/NGC/guardian.co.uk Hunters – such as these men with the carcass of a sitatunga – make canoes from the hollowed-out trunks of rain trees and jackal-berries. People also eat the rhizomes of blue water lilies, hibiscus leaves and berries; other plants are used for wine, soap and to poison fish Photograph: Frans Lanting/Corbis Photograph: Frans Lanting/guardian.co.uk Horses eat sinuous paths through the aquatic vegetation, which supports 10 times more large mammals – including lions, elephants, giraffes, buffalo and antelope – than would be expected in an area of similar rainfall and sandy soil Photograph: Michael Fay/NGC/Getty Photograph: Michael Fay/NGC/guardian.co.uk Most of the 71 fish species are too small for people to eat, but there is a small amount of commercial fishing, and many people, such as this Hambukushu woman and her child, catch talapia and other bigger species for subsistence Photograph: Frans Lanting/Corbis Photograph: Frans Lanting/guardian.co.uk Insects, zooplankton and fish support thousands of often colourful birds, such as this saddle-billed stork Photograph: Theo Allofs/Corbis Photograph: Theo Allofs/guardian.co.uk A Hambukushu village in Botswana. Archeologists believe men and women started to live off the delta at least 100,000 years ago. The human history has been one of frequent migration to new natural resources, or to escape disease, conflict, drought and flooding Photograph: Frans Lanting/Corbis Photograph: Frans Lanting/guardian.co.uk A man herds cattle. About 140,000 people live in the area, many in the town of Maun, whose population is doubling every 11 years. People are increasingly less dependent on farming and more so on salaries, business income, social benefits and subsidies Photograph: Frans Lanting/Corbis Photograph: Frans Lanting/guardian.co.uk These running red lechwe make the delta look pristine, and indeed it is relatively so – but climate change, growing demand for irrigation water upstream in Angola, local contamination from chemicals (such as pesticides used to kill tsetse flies), invasive alien species and the clearing of channels are all threats Photograph: Frans Lanting/Corbis Photograph: Frans Lanting/guardian.co.uk A lioness retreats from a herd of cape buffalo. About 100,000 visitors a year to the delta region make up the bulk of Botswana's tourist economy (the country's second-biggest economic sector, after diamonds), which brings inevitable pressure for unsustainable development Photograph: Beverly Joubert/NGC/Getty Photograph: Beverly Joubert/NGC/guardian.co.uk Another problem is the burgeoning population of elephants, whose decimation of riverside woodland has raised concerns that they could damage the delta's "kidney" system of island trees Photograph: Theo Allofs/Getty Photograph: Theo Allofs/guardian.co.uk African buffalo at twilight. Efforts to preserve the delta must preserve the pulses of flow that sustain the wetting/drying pattern, the channels that constantly redistribute the life-giving water and nutrients, and the other processes that make the area an oasis of freshwater Photograph: Beverly Joubert/NGC/Getty Photograph: Beverly Joubert/NGC/guardian.co.uk A chacma baboon enjoys a mushroom Photograph: Beverly Joubert/NGC/Corbis