When something is submerged, it's under water — like a submarine, a car caught in a flood, or your feet in a wading pool.
Use the adjective submerged to describe something that stays under the surface of the water. The flood in your basement might cause your exercise equipment to be submerged, and you probably snorkel with your face submerged. You can also use submerged to describe something that's covered up. For example, you might try to keep your sad feelings about your dog's death submerged when you're with your friends.
