Grimms fairy Tale-the Light Princess

A Princess runs away from her family because she cannot be held down by gravity. She runs to the nearest river where she jumps in and gains gravity in the water.  Because she feels at home she makes a deal with the spirit of the river to get a dress that allows her to breath underwater. But it comes at a cost; she must never leave the water.  A young prince walks through the forest and sees her. He believes she is drowning so he jumps in to save her and fights the spirit of the river to save her. He then pulls her from the river and after they fall in love she gets back her gravity on land and they marry.