What is an ocean dead zone?
A dead zone is an area in the ocean which does not have any life at all. There are now nearly 150 dead zones all over the world. Some dead zones are small, and some are huge – as large as 40,000 sq. miles. Dead zones are caused by excess nitrogen from fertilizer and sewage washing down rivers into the sea, triggering an explosive growth of plankton which uses up all the oxygen in the water. Because there is no oxygen, everything that cannot swim away dies.
