Floating islands are a common natural phenomenon that are found in many parts of the world. Less commonly floating islands exist as a man-made phenomenon. They are generally found on marshlands, lakes, and similar wetland locations, and can be many hectares in size.
When they occur naturally they are sometimes referred to as tussocks, floatons, or sudds. Natural floating islands are composed of vegetation growing on a buoyant mat consisting of plant roots or other organic detritus.
They typically occur when growths of cattails, bulrush, sedge, and reeds extend outward from the shoreline of a wetland area. As the water gets deeper the roots no longer reach the bottom, so they use the oxygen in their root mass for buoyancy, and the surrounding vegetation for support to retain their top-side-up orientation. The area beneath these floating mats is exceptionally rich in aquatic lifeforms. Eventually, storm events tear whole sections free from the shore, and the islands thus formed migrate around a lake with changing winds, eventually either reattaching to a new area of the shore, or breaking up in heavy weather.
Floating artificial islands are generally made of bundled reeds, and the best known examples are those of the Uros people of Lake Titikaka, Peru, who build their villages upon what are in effect huge rafts of bundled totora reeds. The Uros originally created their islands to prevent attacks by their more aggressive neighbours, the Incas and Collas.
Natural floating islands may have been the source of many "disappearing island" legends, such as those of surrounding the Isle of Avalon.
- Inca Heartland (http://alexuk.com/travel/inca/photos9.html) - A site with numerous pictures of floating artificial islands on Lake Titicaca.
- Tourism Keeping Peruvian Islands Afloat (http://monolith.com.au/travel/peru.html) article by Roderick Eime