Question

After the death way ? the dead body is floting up in on water?

Answer 1

as bodies decompose and gasses are released in the body , the corpse will rise back to surface as a result of buoyancy .

Answer 2

after the death the microorganisms start decomposing the death body which lead to release of all gases in the body and the decomposing of body into simpler substances  by microorganisms make it weight less its density becomes lower and start floating on water after some time of death