Lake Magadi - Soda Lake lies in remote, semidesert surroundings where the daytime temperature rises to 38°C(100°F) and is thick with soda. Natron, which often glows blotchy pink, is marginally milder but larger - 40 miles (64km) long and 10 miles (16km) wide. The heat causes more water to evaporate from these lakes than they get from rainfall, which is as little as 16in (400mm) a year. Scorching soda sludge rings the lake shores; at midday, it can be as hot as 65°C (150°F) to the touch.
Thriving in the water - a significant number of microscopic plants and animals, give the soda lakes their predominant green or pink colours, but the colours change according to fluctuations in their numbers and local conditions. There are billions of algae (minute water plants), and tiny grazing animals such as brine shrimps are so abundant that the water fizzes with air bubbles.
The white of the lakes comes from dried, encrusted soda where the water has evaporated. This soda, chiefly sodium carbonate (washing soda), is washed in from the soda-rich surrounding soil and the soda-ash spewed out by local volcanoes. The amount of soda in the water varies from lake to lake. Lakes Magadi and Natron, at the inhospitable southern end of the valley, neither of which has a water outlet, are the deepest and hottest and have the greatest concentration of soda.
Other soda lakes, such as Bogoria, Nakuru and Elmenteita, are milder and more hospitable to wildlife, largely because of the river outlets that keep the water moving and limit the soda. But they also shrink from evaporation. During the 1950s Elmenteita and Nakuru almost disappeared, leaving the air filled with throat-searing dust.
Scientists believe that underground spring water, forcing its way up through the soda layers in the bed of the Rift Valley, forever enriching the soda content of the lakes. On Magadi, soda has been commercially extracted since early in the 20th century without the supply diminishing. The hot springs and steaming geysers are heated by volcanic rocks. At Bogoria, the scalding water overflows onto the grass, a hazard to visitors.
In Natron and Magadi the hot springs are the only relatively fresh water available and are the home of a dwarf species of tilapia - local fish that has adapted to live in hot water. After the rain, when the soda is diluted, the fish spread rapidly and breed. Millions gather in the shallows, causing the water to erupt with their movement.
In the 1950s, Leslie brown, a British naturalist who was a chief agricultural officer for Kenya, went to Lake Natron to find out if the flamingos seen from the air were able to breed there. To get close enough to observe them, he had to approach on foot for 7 miles (11km) or more.
Starting at dawn, he walked from his camp to the lake edge and set out across the soda crust. The going was firm at first, but after a while, the surface crumbled beneath each step. He began sinking in soft, foul-smelling mud. Walking became harder, every step an exhausting effort. To add to his canvas bag became soured with soda dust.
Despite Brown's powerful build and experience as a wildflower in Scotland, his progress became so hopeless that he had to turn back. Intense heat, dehydration and exhaustion made that return a solid surface he took off his boots, which were filled with soda crystals, and his legs, badly blistered, turned black as they were exposed to air. After the long walk back to his camp, Brown collapsed and was semiconscious for three days in the hospital. It took six weeks and a period of skin grafts for his legs to recover.