FIGURE 41.2 Dead zone. When raw sewage is dumped directly into bodies of water, subsequent decomposition by microbes can consume nearly all of the oxygen in the water and cause a dead zone to develop. Shown here are (a) oxygen concentrations in Gulf Coast waters and (b) a massive fish die-off that occurred as a result of low oxygen conditions in Lake Trafford, Florida.

(a: NASA/Goddard Space Flight Center Scientific Visualization Studio; b: Steven David Miller/Nature Picture Library)