Runoff Pollution:

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When rain falls, it flows along the ground into streams, rivers and eventually, the ocean. When it flows it carries with it things we put on the ground, among them, lawn chemicals and fertilizers. These fertilizers work just as well in the ocean as they do on land, but the results are not good for the sea. These chemicals cause algae to bloom in huge numbers (they are fertilizers, remember?). The algae live a short period, die, fall to the bottom and rot. When they rot, the process ends up taking oxygen out of the water. It causes areas of the ocean to be unable to support life. Scientists call those areas dead zones. There have been dead zones in our survey area. There was even one close to us in Long Island Sound one for a while. This map shows all the known dead zones in the world. It is from NASA and can be found here: