Have you ever tried to order a meal in a restaurant and the waiter couldn't understand you? That's more or less what happened here. The web server couldn't make sense of your request for //www.worldheritagesite.org/connection/Individual+Rivers and declined to serve you.
If you were toying with the URLs, use the links provided in the lists and menus. If you were trying to break our system, please stop.
If this persists, contact us via the forum or by mail. We will come around to it. But it may take a while.