More than thirty years after the passage of the Clean Water Act, a large area of low oxygen or hypoxia, absent of most marine life and threatening to inexorably change the biology of the region, continues to form in the Gulf of Mexico during periods in the summer off the coasts of Louisiana and Texas. The hypoxia is primarily caused by excess nutrientsoriginating from the great productivity of Middle American cities, farms, and industrieswhich cause extensive growths of algae that deplete the oxygen in the water when they die, sink to the bottom, and decompose. The condition is exacerbated by the stratification of the water columnthe result of warmer, low salinity surface waters that isolate the organic-rich bottom waters from the surface and prevent oxygen exchange with the atmospherewhich occurs where the Mississippi River meets the Gulf of Mexico.