Every summer, marine biologists have come to expect the formation of a huge band of nearly lifeless ocean off the coast of Louisiana in the Gulf of Mexico. This area, called a "dead zone", kills or drives off fish, crustaceans, and other sea life because it is so depleted of oxygen.

The condition of oxygen depletion is known as hypoxia. Hypoxia results in dead zones worldwide, but the one in the Gulf of Mexico is the largest. The size of the dead zone in the Gulf changes every year. In 1988, a year of drought, the dead zone was relatively small. In 1993, a year of flooding on the Mississippi River, the dead zone was quite large. In the summer of 1999, the dead zone in the Gulf of Mexico was 20,000 square kilometers, an area about the size of New Jersey.

  !   Move your cursor over the satellite image to see the area of the dead zone in 1999. Click the highlighted zone to see a photograph of the dead zone viewed from a boat.