Jim Henson's The Storyteller: Sirens #4

In this German tale, Lorelai is a river nymph, born to the Rhine River, living in the shadow of a prosperous town called Wochara. But at the heart of Wochara’s prosperity lies a secret deal that Lorelei and the people of Wochara struck a long time ago. Every year, Wochara sends Lorelei a young man who becomes her husband for the year, living in comfort and luxury in her wondrous palace, while fat nuggets of gold wash up on the town shores. But not everything is as it seems and when she selects a young man who already has a lover, the deal between the people of Wochara and Lorelai is in jeopardy forever.