The Collaborative International Dictionary of English v.0.48:

Water god \Wa"ter god`\ (Myth.)
   A fabulous deity supposed to dwell in, and preside over, some
   body of water.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "water god":
   Davy, Davy Jones, Dylan, Neptune, Nereid, Nereus, Oceanid, Oceanus,
   Poseidon, Thetis, Triton, Varuna, mermaid, merman, sea devil,
   sea god, seaman, siren