2010-06-16 [Serwa]: In Greek mythology, nymphs are spirits of nature. They are minor female deities and the protectors of springs, mountains, and rivers. Nymphs are represented as young, pretty girls. Each subtype presides over a certain aspect of nature. Depending of their habitat, there are: Dryads (forests), Naiads (springs and rivers), Nereid (the Mediterranean), Oceanids (the sea) and Oreads (mountains), Limoniads (meadows), Limniads (lakes, marshes and swamps) and Napaea (valleys). They were worshipped in a nymphaeum, a monumental fountain which was raised in the vicinity of a well. The male counterpart of a nymph is the satyr.

Source: http://www.pantheon.org/articles/n/nymphs.html
(source contains more info on the different kinds of nymphs)