A dead zone is a part of the ocean with a low oxygen count. These dead zones are highly dangerous to marine life.
How are dead zones made?
Dead zones are made when fertilizer runs off the land into the rivers then into the oceans. All this fertilizer makes algae grow faster. When there is a lot of algae growing in one place it is called an algae bloom, when this algae dies it takes up oxygen and now you have a low oxygen area/dead zone.
Why is this a problem for ocean life?
This is a problem because when there is no oxygen in the water everything suffocates.