Krishna once hid in the Yamuna, the Gopis desperately sought him everywhere.
Finally they asked the Yamuna if she knew where he might be. The Yamuna felt pity and asked Krishna to leave his hiding place.
In exchange, the Gopis gave her their scarfs (Chunri). Manorath means wish.
On Chunri Manorath women give the Yamuna a scarf to thank her for fulfilling a wish.