The 80 meter long passenger ship Princess went aground on the Elbe River near Wittenberg, Germany.   The Princess had 87 passengers and a crew of 18 when it became stuck in the river due to a low river tide of 1,30 meters.   The passengers were transferred to the Lutherstadt Wittenberg and taken back to the harbour at Wittenberg.   No reports of injuries.  After unloading passengers, luggage, water ballast, and some assistance from a tug, the vessel was refloated.  River traffic is closed due to the build up of sand caused by the Princess refloating.  A dredger has been requested to reopen river traffic.