The Starnbergersee, a lake near Munich, is mentioned on line 8.
On 13 June, 1886, King Ludwig II of Bavaria, and a companion were drowned here under mysterious circumstances.
You can put the cross reference list for death by water here.
Members of Bavaria's Wittelsbach royal family show up here and there in The Waste Land, either mentioned outright or as possible allusions. See these Miscellanea pages (ordered as they appear):
For much more information on Marie, her aunt, the Empress, her aunt, the Queen, her archduke cousins, her cousin King Ludwig and other royal and imperial family members visit this webpage elsewhere on this website: http://world.std.com/~raparker/exploring/thewasteland/exmarie.html