Right beneath the hole, the water is only about waist deep. In the light of Kuja's orb, they can just about see the walls on their right and left, but the far end of the space remains unseen, shrouded in pitch black darkness.

Should they wade in further, they'll notice the floor is ever so slightly angled downward. They should still be able to walk a decent distance without needing to swim, but the shorter Heroes may find themselves struggling somewhat.