Nymphs

Nymphs live for thousands of years, and yet remain adolescent girls, forever; dazzling in beauty and youth.  Nymphs guard all the natural places of the earth: from fresh running streams, to the oceans, flowers, clouds, the sun, the wind - find a full list here  They were made as close-kin to gods and as protectors of nature.

Nymphs belong to specific places, and not only are they often named after those places, but also, the feel of that place describes the nymph.  For example, a dark, misty dam would probably have a dark, troubled nymph presiding over it.  Nymphs usually adopt some of the element of their habitat. As an idea, the costumes of the Sea Nymphs (for example) could be blue and green with ocean foam as a trimming.  

They may marry humans; it seems through their own strong will. If the nymph does not have wings, it would be easy for her to trick a man into believing that she is a human girl of unearthly beauty, not a faerie.  Their sons become remarkable heroes.

Mermaids, through many legends, are depicted as being able to woo a man through her singing to his death, and that the sight of a mermaid while out at sea was a bad omen.  It is not difficult to see where the word 'nymphomaniac' originates from!

On the contrary, nymphs have been known to have amazing healing powers from nature and may be very kind to a human in need.