water witch

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One who claims to be able to find underground water by means of a divining rod; a dowser.

from The Century Dictionary.

• noun A witch who dwells in the water; a water-nixy.
• noun A person who pretends to have the power of discovering subterranean springs by means of a divining-rod.
• noun One of several water-birds noted for their quickness in diving, as a kind of duck, the buffle-headed duck, Clangula or Bucephala albeola, and especially various species of grebes or didappers, as the horned grebe, Podicipes cornur tus, or the pied-billed dabchick, Podilymbus podicipes. See cuts under buffle, grebe, and Tachybaptes.
• noun The stormy petrel, or Mother Carey's chicken. See cut under petrel.

from the GNU version of the Collaborative International Dictionary of English.

• Prov. Eng., Prov. Eng. The dabchick.
• Prov. Eng. The stormy petrel.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The dabchick.
• noun UK, dialect The stormy petrel.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun someone who uses a divining rod to find underground water