In a vast ocean region, phosphorus levels have doubled in the past few decades due to agricultural runoff pouring out of a large river nearby  The phosphorus stimulates the growth of plankton near the ocean surface  Decaying plankton fall to the ocean floor, where bacteria devour them, consuming oxygen in the process
Due to the resulting oxygen depletion, few fish can survive in this region
The agricultural runoff pouring out of the river contributes to the growth of plankton near the ocean surface.