When a person is alive and is drowning in water, he does not drown in water until water enters his lungs through his mouth and breath, then when a person drowns and dies like you Know that after death the process of decomposition begins in which the bacteria in our body (especially in our intestines) decompose the body and the surrounding bacteria and other microbes also take part in this process and gas is formed from this decomposition. Which inflate the chest and abdomen of the corpse, as the density of the gas is less than that of the water, then the corpse comes to the surface of the water as an air balloon floats on the water
These gases include methane, carbon dioxide and other gases. It also depends on the conditions under which these gases will be formed and the body will rise above it. And the whole body does not come up together, but first the organs like the abdomen come up where there is more speed and more decomposition. Sometimes if the corpse stays up for a long time, these gases are released back, which causes the corpse to go back into the water.