In Ukrainian belief, the moon was called the rusalka’s sun. During the Green Holidays, when rye was in flower, rusalki came out of the water to swing on tree branches, comb their hair, dance, and cry like cats.

A rusalka’s comb was thought to give her the power to flood an entire place as she combed her wavy hair. But if her braids dried out, she died at once — which was why she could not stray far from water without the comb.

Source: V. P. Miloradovych, Ukrainian Witch: Essays on Ukrainian Demonology (Kyiv: Veselka, 1993)., “Rusalki, Mavky, and Loskitnytsi.”