From WordNet (r) 3.0 (2006) [wn]:
underwater
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]