Lake Natron

Three quarters of the world’s lesser flamingos hatch on water that calcifies the dead

Lake Natron lies in the Gregory Rift, the eastern arm of the East African Rift, in northern Tanzania, its northern tip crossing into Kenya. It is up to 57 km long and 22 km wide but less than three metres deep, fed by the Southern Ewaso Ng'iro River out of central Kenya and by mineral-rich hot springs, with no outlet but the sky. Temperatures at the lake often top 40°C, and the water can reach 60°C. The rocks around it are Pleistocene trachyte lavas rich in sodium carbonate and poor in calcium and magnesium, so as the water evaporates it concentrates into a caustic soda brine, leaving crusts of natron and trona behind. Its pH has been measured at 10.5, nearly as high as ammonia, and by some accounts above 12.

In the dry season, as the salt climbs, cyanobacteria bloom and turn the open water deep red and the shallows orange, and the surface crust pink. Few things live in it. A handful of tilapia survive in the less salty lagoons at the hot spring inlets, retreating into the streams when the lake rises, and nothing that would eat a flamingo egg can cross the lake to reach the nests on its seasonal salt islands. Natron is the only regular breeding ground in East Africa for some 2.5 million lesser flamingos, and about 75 percent of all the world's lesser flamingos are born here.

The lake is also famous for its dead. In 2011 the photographer Nick Brandt found that migrating birds often crash into its glassy, reflective surface, and in the dry season their bodies, desiccated and preserved by the soda, wash up along the shore, sometimes a hundred finches in fifty yards. Working with locals for about three weeks, he collected the finest specimens, swallows, doves, a fish eagle, and posed them on branches for a series called The Calcified, insisting the bodies were exactly as he found them. The water stripped the ink off his film boxes within seconds, and even the tiniest cut stung badly.

Industry has had its eye on the lake. In 2008, after a campaign by more than fifty East African conservation groups, Tata Chemicals dropped plans for a soda ash plant on the shore; Tanzania has since revived plans to mine soda ash with an operation more than 40 miles away. A proposed hydroelectric plant on the Ewaso Ng'iro could also upset the lake's balance. The Lake Natron Basin has been a Ramsar wetland of international importance since 2001, and campgrounds near the shore serve as the base for climbing Ol Doinyo Lengai.