Lake Eyre is the lowest point in Australia, 15.2 meters below sea level, and at the center of an immense drainage basin encompassing one seventh of the continent's land surface. However, central Australia is so arid that Lake Eyre is usually dry. Salt crusts, formed through evaporation of the lake waters, are clearly visible in this shuttle photograph (light pink); the red colour of the water is due to the presence of brine-tolerant algae. The ancient desert floor around the lake is stained red-brown due to the presence of a residue of iron oxides following millions of years of weathering and erosion.