created their islands to prevent attacks by their more aggressive neighbours, the Incas and Collas. The Aztec capital, Tenochtitlan, was surrounded with chinampas, small artificial islands used for agriculture known as "floating gardens" (though not really floating). Floating gardens on a large scale have been demonstrated with aquaponics systems in China growing rice, wheat and canna lily on islands, with some installations exceeding . Spiral Island was a more modern one-person effort to build an artificial floating island, on the Caribbean coast of Mexico. Modern artificial islands mimicking the floating reedbeds of the Uros are increasingly used by local governments and catchment managers to improve water quality at source, reducing pollutants in surface water bodies and providing biodiversity habitat. Examples include Gold Coast City Council in Australia. Artificial floating reedbeds are commonly anchored to the shoreline or bottom of water body, to ensure the system does not float away in a storm event or create a hazard. During World War II, the British Project Habakkuk proposed the construction of aircraft carriers made of ice-like Pykrete. Its size and speed made it more of an artificial iceberg or island than a ship. Commercial development of floating islands has begun taking place. Floating habitat islands were installed with salicornia salt marsh plants at Sydney Olympic Park Authority in 2011 providing nesting sites for local and migratory birds including black swans, black-winged stilts, red-necked avocets, Pacific black ducks and chestnut teals, using the Aqua Biofilter product. The world's largest vegetated floating islands in size were installed in 2004 using Aqua Biofilter™ product with Canna (plant) at Lake Tai, China using materials including a combination of polyurethane open cell filter foam, closed cell polyethylene flotation foam, bamboo and coconut fibre filter foam mix with wicking ability to supply water to plant roots. A commercially produced floating island was installed in the river otter enclosure at Zoo Montana in 2007. In 2009 and the beginning of 2010, a few larger islands were launched to provide nesting habitat for Caspian tern colonies. The largest of the islands, at a record-setting , was launched into the water at Sheepy Lake. These islands are a collaboration between the United States Army Corps of Engineers, Oregon State University, and Floating Islands West, a Floating Island International license holder. A recent US Army Corps of Engineers project was built in The Hideout, Pennsylvania as part of a watershed management project.