Dead Zones: Where Oxygen Disappears

When excess nitrogen and phosphorus hit coastal waters, they trigger algal blooms — massive explosions of algae growth. When those algae die, bacteria decompose them and consume enormous amounts of dissolved oxygen. The result is a dead zone: an area where oxygen levels drop so low that most marine life either flees or suffocates.

The Gulf of Mexico dead zone, fed by Mississippi agricultural runoff, regularly exceeds 15,000 square kilometers. Globally, over 400 dead zones have been identified. The Baltic Sea, Black Sea, and Chesapeake Bay all suffer chronic oxygen depletion.