A dead zone is a large area of ocean without fish or plant life. Many dead zones are near coasts since rivers carry fertilizer runoff.
How it happens:
- Fertilizers run off of lawns and farm fields
- Fertilizer promotes algae growth in the water that the fertilizer is in contact with
- Lakes, rivers, and bays become clogged with algae and aquatic plants
- These organisms eventually die and decompose
- Decomposition uses up dissolved oxygen in water
- Large numbers of plants and marine animals cannot thrive without oxygen
- A dead zone develops
Dead zones off the coasts are indicated by
red dots on this diagram.