Your emotions or inner state (turbulence, tranquility, etc.).
The unknown.
An area that you feel holds secrets (perhaps within yourself).
Swimming or floating in a body of water can represent freedom from your usual limitations or stresses.
A body of water rising over your head (or you being pulled under water) can represent a feeling of overwhelm or “trying to stay afloat” in real life.
A calm body of water can represent peace or relaxation.
For more clues, consider the context and condition of the water.
See also: Water; Waves; Flow or River; Swimming; Floating; Underwater; Flood; Pool