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tiny amounts of these substances can cause serious harm. Such chemicals, for example, contaminate the Great Lakes.

To emphasize the importance of decreasing the water pollution, we need to understand what the major effects of water pollution are. We need to understand that water pollution is very dangerous and can cause serious harm. There are many different effects of water pollution.

So-called run-off pollution is damaging to plants. It includes many small sources, like septic tanks, cars, trucks and boats, plus larger sources, such as farms, ranches and forest areas. Millions of motor vehicle engines make daily, one-drop-at-a-time "oil spills" onto roads and parking lots, which add significantly to run-off pollution. Some water pollution actually starts as air pollution, which settles into waterways and oceans. Dirt in general can be a pollutant and the rain that runs off the land picks up dirt and carries it into the water. There, the dirt can settle and keep sunlight from reaching aquatic plants, which will die if they do not get enough sunlight.

Fertilizers and other chemicals are even more damaging than run-off pollution. When rainwater runs off farm areas where fertilizers or pesticides are used the fertilizers can get into the water. When the polluted rainwater reaches rivers or lakes, the plants in there will grow quicker. If there are more plants, there grow also more bacteria because bacteria eat dead plants. The bacteria need oxygen to survive which, in turn, affects the fish or other animals living in the water. It effects the animal living in the water because there will be less oxygen left for them.