After railroads largely superseded them, in the 20th century, they were more frequently used for entertainment excursions, sometimes for several hours, than for passage among riverfront towns.An unusual situation occurred on the Potomac River in the mid-20th century due to a quirk in the state border between Maryland and Virginia.There was no law in Maryland against having casinos on land, but this spared Virginia residents the trouble of having to cross the river, which could involve driving a significant distance out of the way to the nearest bridge.By 1998, "according to the state Gaming Commission, just three of the 16 operations comprising Missouri's $652-million riverboat gambling industry [were] clearly on the main river channel."Most of Mississippi's Gulf Coast riverboat casinos have been rebuilt on beachfronts with solid foundation systems since the hurricane.