National Geographic : 1984 Jan
pigment as needed to protect against the sunlight drenching these crystalline waters. In the fresher water of Ewens Ponds, great bouquets of the water buttercups climb stalks of Triglochin (above). Found in fresh waters across Australia, Triglochinproduces an edible, potato-like tuber Australia'sSunken Realm still harvested by Aboriginals in the north. The fantastic water clarity of the Mount Gambier sink holes results from several fac tors. The holes are fed from aquifers holding rainwater that fell decades-even centu ries-ago, and that has been filtered through miles of limestone. The high level of calcium that limestone adds causes the silty detritus from dead plants and animals to cling together and settle quick ly to the bottom. Abundant bottom vegetation in the shal low sinkholes also helps bind the silt. And the rapid turnover of water prohibits stagnation.