At the beginning of every summer a phenomenal algae (phytoplankton) bloom in the Gulf just off the mouth of the Mississippi creates an area of low oxygen. Fish flee the "dead zone" in search of more hospitable waters. Other organisms are trapped and die. As Fall arrives the bloom stops and gradually life returns.

Each year the "dead zone" grows larger. In 2006 it reached 8,000 square miles, the size of New Jersey. It spread westward from the mouth of the river to Texas. It affects local fishing and the long term effects have not been studied. There is no information about whether there is a critical size which once reached will not fully recover by the beginning fo the next bloom. The Mississippi Gulf dead zone is not unique as there are hundreds worldwide.

Scientists studying the phenomenon attribute it to the impact of fertilizer runoff from farms drained into the river. Fertilizer, summer temperatures and freshwater layers encourage the algae bloom. As the algae die and decompose they consume the oxygen in the water. Layers of freshwater near the surface retard the uptake of oxygen by the deeper saltwater layers.

Cooler temperatures, reduced river volume and less sunlight experienced in the Fall allow the Gulf to recover. Efforts to reduce the problem, primarily by reducing the amount of fertilizer in the river by 30% have been stymied by the Bush Administration. Funding has been diverted, but even more importantly efforts to produce more corn for ethanol have placed more land in cultivation and increased the fertilizer load of the river.