Floating and sinking

Sinking

Is the density of a body higher than the density of the fluid it is submerged in, the body sinks to the bottom. Stones and massive iron blocks for example do not float; they sink. In this case, the gravitational force of the body is greater than the gravitational force of the displaced water and therefore greater than the buoyant force which acts on it.
There are even fish which sink to the bottom!

Picture above:
Not all fish are able to float in the water. Many species of flatfish loose their swim bladder while developing. They thereby loose the ability to change their volume and their density. Their density becomes greater than the density of the surrounding water, they have to remain almost permanently on the bottom.