Source : Webster's Revised Unabridged Dictionary (1913)

Subaquatic \Sub`a*quat"ic\, Subaqueous \Sub*a"que*ous\, a.
   1. Being under water, or beneath the surface of water;
      adapted for use under water; submarine; as, a subaqueous
      helmet.

   2. (Geol.) Formed in or under water; as, subaqueous deposits.

Source : WordNet®

subaqueous
     adj : growing or remaining under water; "viewing subaqueous fauna
           from a glass-bottomed boat"; "submerged leaves" [syn: {subaquatic},
            {submerged}, {submersed}, {underwater}]