In nature, there are bodies of water that are called dead zones because of the barrenness or even extinction of almost all life. The cause of the dead zones in the water is because of the lack or non-existence of oxygen in the water, there are many things that cause this to happen. 

The most common cause of the depletion of oxygen in the water is the decaying algae which consume oxygen in its decaying process causing the water to lose some of its oxygen, but when there is a lot of algae it will lose a lot. The cause of the algae blooms or population booms is usually because of an overabundance of nutrients in the water for the algae to eat causing a boom, which will cause barrenness and death because of the loss of oxygen.

One of the well-known examples of the dead zones occurring is in the Gulf of Mexico, occurring because of the overabundance of nutrients from the sediments of the Mississippi River.