Russalki

Russalki, in Slavonic mythology, were nymphs of supernatural beauty, who resided in brooks, rivers, and seas. They oftened bathed in some sparkling fountain, sported on the grass of some sunny meadow, swung to and fro on the waving trees, or combed their long green hair, and might then be overheard; but woe to him who should so observe them, for they rarely gave their love to any favored swain, and he who had once seen them could afterwards discover no attractive features in a woman of earthly mold.