Lake Natron, Tanzania, satellite image. North is at top. This highly alkaline lake is located in Africa's Great Rift Valley. It is considered to be the world's most caustic lake, though it still contains fish that have adapted to the conditions. The orange colour of the salt crusts is due to red pigments from salt-loving (halophilic) blue-green algae, which provide colouring and food for the flamingoes that feed here. This lake was added to the Ramsar List of Wetlands of International Importance in 2001. This image, around 40 kilometres across, was obtained by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA's Terra satellite, on 8 March 2003.