A water park (also waterpark, water world, aquapark) is an amusement park that features water play areas such as swimming pools, water slides, splash pads, water playgrounds, and lazy rivers, as well as areas for floating, bathing, swimming, and other barefoot environments. Modern water parks may also be equipped with some type of artificial surfing or bodyboarding environment, such as a wave pool or flowrider. History Water parks have grown in popularity since their introduction in the late 1940s and early 1950s. The United States has the largest and most concentrated water park market, with over 1,000 water parks and dozens of new parks opening each year. Major organizations are the IAAPA (International Association of Amusement Parks and Attractions) and WWA (World Waterpark Association), which is the industry trade association. Water parks which emerge from spas tend to more closely resemble mountain resorts, as they become year-round destinations. For example, Splash Universe Water Park Resort is themed to match the community in which it is located. The theme is intended to enhance the community's destination appeal. Therefore, the amusement and leisure-time industry is becoming more concentrated, as winter sports are becoming common themes in summertime water recreation. A process of concentration can be observed in the hybrid versions of theme-, amusement-, and water parks. Some water parks are more spa-oriented. For example, SchwabenQuellen has no water slides; it has instead many saunas, steam rooms, "adventure showers", and relaxation-oriented water play areas. In the 2000s, an effort was made to reduce long waiting lines by introducing conveyor belts to lift passengers or use water jets. An unusual feature at a water park is ice skating. Deep River Water Park in northwestern Indiana features ice skating, made possible by cooling pipes installed under their massive plaza. Indoor water parks Some of the first indoor water parks are at Duinrell (The Netherlands, 1984), Nautiland located at Haguenau (France, 1984), the Aqua Mundo at Center Parc De Eemhof located at Zeewolde (The Netherlands, 1980) and (Switzerland, 1977). In 1986 World Waterpark was open in Edmonton, Alberta, Canada at the West Edmonton Mall. It is in 2016 the largest indoor water park in North America. Tropical Islands Resort (Germany), with an area of , is in 2016 the largest indoor water park in the world. With five indoor water parks, Wisconsin Dells, Wisconsin has been dubbed the "Water Park Capital of the World". It showcases