Nixes are water spirits who live in lakes and rivers.
They are beautiful humanoid creatures who are often depicted with green
teeth and fish's tails. However, they can assume many forms, including
that of humans. In human shape, they can always be recognized by the
permanently wet hem of their clothing. They are known to lure humans into
the water--they often steal humans for spouses. Nixes are also known to
dance on the water just before a human drowns there.
Kneightley, Thomas. The World Guide to Gnomes, Fairies, Elves, and
Other Little People. New York: Avenel Books, 1978.