For most of the year, the Gulf of Mexico is teeming with marine life, from tiny crustaceans to massive whales. But every summer, disaster strikes. Around May, animals begin to flee the area. And soon, creatures that can't swim or can't swim fast enough begin to suffocate and die off in massive numbers. What's going on? Kate Slabosky dives into the lethal conditions that create dead zones. [Directed Mette Ilene Holmriis, narrated by Adrian Dannatt, music by Stephen LaRosa].