The Collaborative International Dictionary of English v.0.48:

Submerge \Sub*merge"\, v. t. [imp. & p. p. Submerged; p. pr. &
   vb. n. Submerging.] [L. submergere, submersum; sub under +
   mergere to plunge: cf. F. submerger. See Merge.]
   1. To put under water; to plunge.
      [1913 Webster]

   2. To cover or overflow with water; to inundate; to flood; to
      drown.
      [1913 Webster]

            I would thou didst,
            So half my Egypt were submerged.      --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

submerged
    adj 1: beneath the surface of the water; "submerged rocks" [syn:
           submerged, submersed, underwater]
    2: growing or remaining under water; "viewing subaqueous fauna
       from a glass-bottomed boat"; "submerged leaves" [syn:
       subaqueous, subaquatic, submerged, submersed,
       underwater]