A body of water such as an ocean, lake, etc. can represent:
The context of your life—meaning the setting and situations within which the your life takes place—"your world"
The unknown or a huge, deep area that you feel holds secrets
You 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 in real life.A calm body of water can represent peace or relaxation.Water that is flowing or changing shape can represent change in the dreamer's life—possibly out of the dreamer's control.