Initially, bodies will likely sink to the bottom, but as bodies decompose and gasses are released in the body, the corpse will rise back to the surface as a result of buoyancy.
The reason that living human beings naturally float is because of the air in our lungs. The air acts as a buoyant force for the body, making it impossible for you to simply lie down at the bottom of a swimming pool. In the case of a corpse, however, they have no control over whether their lungs fill up or not. If the corpse falls in the water facedown, they might never sink to the bottom, as there will be no real chance for the air to escape from the lungs. However, if a corpse is put into the water on their back, air can escape, water can take its place, and the body will quickly sink.
If a person drowns, they don’t necessarily die because water fills up their lungs; often, the body will asphyxiate itself because the windpipe closes up against the presence of water. In this case, a body could potentially float for longer periods before eventually sinking to the bottom. However, given that almost every dead body falls beneath the surface eventually, once all the air is expelled from the lungs
