The Nöck (or Nix, Neck, Näck, or Nickert) is a protective water spirit who lives in lakes, ponds, springs, wells and even drops of water.  The word is likely derived from Old High German nihhus , niccus or nichessa (“water spirit”), although an alternate theory traces its origin to the Latin necare (“killing”) or the Old English nicor (“water demon”).

Image:
Theodor Kittelsen: Der Nöck (1887)