Resuscitating the Gulf’s dead zone

Every spring for many years now, a dead zone has formed in the Gulf of Mexico just south of the Mississippi River Delta. This patch of water contains less than 2 milligrams of oxygen per liter, which is too little to sustain most aquatic life. For the past 5 years, this dead zone reached its maximum size—on average, 5,500 square miles, or roughly the size of Connecticut—around midsummer and disappeared in the fall.