From the Bureau of Almost Forgotten Footage:

I was doing a search in our video footage files and came up a clip I shot several years ago and proceeded to forget. It was a rainy day aboard Peter Deilmann Cruises Mozart, a luxe riverboat the plies the Danube...which is really blue at times and quite beautiful.  I fixed my camera on my cabin window and watched scenes along the riverbank dissolve before me. The vocal of Strauss' Blue Danube was recorded by Frieda Hempel in 1907.