Well, as if we needed one more reason to get our environmental act together, a recent U.N. report warns that the number and size of dead zones in the ocean is increasing.

Dead zones are regions of oxygen-deprived water, where nothing can live. They're caused by an excess of nutrients--usually nitrogen--released into the water. When sewage, farm fertilizers, and emissions from vehicles and factories get washed into the ocean, you get what experts call a "nitrogen cascade." Tiny free- floating organisms known as plankton feed on all that untreated nitrogen, and multiply to such an extent that they deplete the oxygen supply in the water.

While fish may be able to swim away and avoid suffocation, slower-moving and bottom-dwelling creatures like lobsters, clams, and oysters often can't. Also, the ocean might be a large place, but right now there are 146 known dead zones, some of which span tens of thousands of square miles. One of the worst is where the Mississippi River drains into the Gulf of Mexico, and dumps fertilizer runoff from the Midwest.

To stop dead  zones from further expansion, we can reduce nitrogen emissions from cars and factories, and implement better sewage treatment. We can plant new forest and grasslands to soak up extra nitrogen and keep it out of the water. And we can develop alternative energy sources that aren't based on burning fossil fuels.