Salt lakes are a fairly common sight in Australia. They form as the water they contain evaporates, leaving behind the salts that are dissolved in it. Commonly, salt lakes have a remarkable purple colour, which is due to the presence of microscopic, salt loving bacteria, called halobacteria. These bacteria produce a red carotenoid pigment, which is similar to that found in tomatoes, red peppers, pink flamingos, and in many colorful flowers and autumn leaves. For more infomation and some spectacular images have a look here.