In this video segment adapted from the independent film Big River: A King Corn Companion, the filmmakers explain how agricultural runoff from the Midwest has contributed to a massive "dead zone" in the Gulf of Mexico. A cornfield treated with conventional chemical fertilizer promises a bumper crop, but chemical runoff from the farm enters the Iowa River, eventually draining into the Mississippi River and the Gulf of Mexico. In the Gulf, these dissolved nutrients allow algae to flourish. The algae's decay depletes the water of oxygen, creating a dead zone where shrimp and fish are starved of oxygen and die. A background essay, discussion questions, and standards correlations are also provided.