It's important to say that Heinrich Heine wrote the famous poem, Die Lorelei, which, if perhaps not the actual origin of the legend (I don't know enough to say) is so famous that it has in effect become the legend. I think the Nazis tried to create a myth that it was an anonymous folk poem, in an attempt to expunge Heine's name.
In German legend, a beautiful woman with long blonde hair who sat on the Lorelei rock and with her fine singing distracted boatmen, so that they drowned when their ships foundered on the rock. See also siren.
River, river have mercy, take me down to the sea For if I perish on these rocks, my love no more I'll see I've thought of you in far-off places, puzzled over lipstick traces So help me God, I will not cry--and then I think of Lorelei --"Lorelei," the Pogues, c. 1989 Phillip Chevron