Lake Natron is a salt and soda lake in the Arusha Region of northern Tanzania. The lake is close to the Kenyan border and is in the Gregory Rift, which is the eastern branch of the East African Rift. The lake is within the Lake Natron Basin, a Ramsar Site wetland of international significance.

Lake Natron is fed principally by the Southern Ewaso Ng’ iro River, which arises in central Kenya, and by mineral-rich hot springs. It is quite shallow, less than three metres (9.8 ft) deep, and varies in width depending on its water level. The lake is a maximum of 35mi long and 14mi wide. The surrounding area receives irregular seasonal rainfall, mainly between December and May totalling 31 inch per year. Temperatures at the lake are frequently above 104 °F.

The color of the lake is characteristic of those where very high evaporation rates occur. As water evaporates during the dry season, salinity levels increase to the point that salt-loving microorganisms begin to thrive. Such halophile organisms include some cyanobacteria that make their own food with photosynthesis as plants do. The red accessory photosynthesizing pigment in the cyanobacteria produces the deep reds of the open water of the lake and the orange colors of the shallow parts of the lake. The alkali salt crust on the surface of the lake is also often colored red or pink by the salt-loving microorganisms that live there.

Salt marshes and freshwater wetlands around the edges of the lake do support a variety of plants.
The lake is the only regular breeding area in East Africa for the 2.5 million lesser flamingoes, whose status of “near threatened” results from their dependence on this one location. When salinity increases, so do cyanobacteria, and the lake can also support more nests. These flamingoes, the single large flock in East Africa, gather along nearby saline lakes to feed on Spirulina (a blue-green algae with red pigments). Lake Natron is a safe breeding location because its caustic environment is a barrier against predators trying to reach their nests on seasonally-forming evaporite islands. Greater flamingos also breed on the mud flats.

Newly discovered fossil footprints at a site in northern Tanzania on the shore of Lake Natron capture a moment in time around 120,000 years ago when a band of 18 humans—early members of our own species, Homo sapiens—traipsed across wet volcanic ash to an unknown destination.

Footprints are extremely rare in the human fossil record, and highly prized for the unique information they can reveal about the anatomy and behavior of our ancient relatives. Richmond and his colleagues found the new prints—more than 350 in all—in 2010 at the site, called Engare Sero. No animal prints were among them.