Paddlewheel riverboats had long been used on the Mississippi River and its tributaries to transport passengers and freight. After railroads largely superseded them, in the 20th century, they were more frequently used for entertainment excursions, sometimes for several hours, than for passage among riverfront towns. They were often a way for people to escape the heat of the town, as well as to enjoy live music and dancing. Gambling was also common on the riverboats, in card games and via slot machines. When riverboat casinos were first approved in the late 20th century by the states, which generally prohibited gaming on land, these casinos were required to be located on ships that could sail away from the dock. In some areas, gambling was allowed only when the ship was sailing, as in the traditional excursions. They were approved in states with frontage along the Mississippi and its tributaries, including Illinois, Indiana, Louisiana, Mississippi and Missouri. Illinois also allowed limited riverboat casinos in the Chicago metropolitan area, which has a Mississippi River connection through the Chicago Sanitary and Ship Canal, while Northwest Indiana has three 'riverboat' casinos in harbors along Lake Michigan.
