Water parks have become increasingly popular since they began in the 1950's. The United States has the largest and most concentrated water park market, with over a thousand water parks currently and dozens of new parks opening each year.
Indoor Water Parks-
Indoor water parks were a phenomenon that started in the Wisconsin Dells in the 1990s but have since caught on quickly in many areas. Usually resort hotels featuring massive indoor water parks that are often reserved exclusively for overnight guests, companies like Great Wolf Resorts/Great Wolf Lodge and Kalahari Resorts have branched out from their origin in the Dells to open new locations around the country. The largest indoor water park in the United States is the Kalahari Resort in Wisconsin Dells, Wisconsin, which opened in May 2000.
Waterparks.com directory of water parks
IndoorWaterParks.net directory of indoor water parks
International Association of Amusement Parks & Attractions
With eighteen indoor water parks, Wisconsin Dells, WI, is recognized as the "Water Park Capital of the World." It boasts America's largest indoor and outdoor water parks -- Noah's Ark and Kalahari Resort.