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Mississippi river map. © TNC

The Mississippi River and its tributaries drain 41 percent of the United States and carry the nutrients that cause the Gulf’s dead zone.

Extremely heavy rains and melting snows washed massive amounts of nutrients—particularly nitrogen and phosphorus—from lawns, sewage treatment plants, farm land and other sources along the Mississippi River into the Gulf of Mexico. Once in the Gulf, these nutrients, which are required for plant and crop growth, trigger algae blooms that choke off oxygen in water and make it difficult, if not impossible, for marine life to survive.

The National Oceanic and Atmospheric Administration, or NOAA, which funded the scientists' research, estimates that the dead zone costs U.S. seafood and tourism industries $82 million a year. The impact could be devastating to the Gulf's seafood industry, which accounts for more than 40 percent of the nation's seafood. Louisiana is second in seafood production only to Alaska.

Because fish and other commercial species usually move out to sea in order to avoid the dead zone, fishermen are forced to travel farther from land—and spend more time and money—to make their catches, adding stress to an industry already hurt by hurricanes and the oil spill. Those species that can't move—or can’t move fast enough—die off, leading to the name “dead zone.”

A team of NOAA-funded scientists from the Louisiana Universities Marine Consortium, Louisiana State University and the University of Michigan recently analyzed nutrient runoff from the recent floods and predicted the dead zone in the Gulf would reach historic proportions. Fortunately, their findings show the dead zone didn't hit an all-time record, but the news was nothing to celebrate. The report underscores the need to invest in our natural resources. The Mississippi River, its tributaries and floodplains, and the Gulf are an inner-connected system that affects—and is affected by—people. We must work collaboratively to find solutions that address the connectivity of this system—solutions that benefit people and nature. Learn how the Conservancy is working to reduce the Gulf's dead zone.

By Jay Harrod, communications manager, North America. Jay can be reached at jharrod@tnc.org.