2. What constitutes pollution?  Any substance which doesn’t belong in the water and causes harm.

3. Sources of Pollution  Pollution can come from a variety of sources.  Point sources: A specific source of pollution which can be easily identified.  Non-point Sources: A widely spread out source of pollution which cannot be easily identified.

4. Pollution in the Food chain

5. Human Wastes  Cities and urban areas produce huge amounts of waste materials.  Most wastes are filtered and removed with water treatment plants.  Serious flooding can cause drains to overflow and spill into surface water.

6. Industrial Wastes  Many factories and industries produce large amounts of waste.  Chemicals: Toxic wastes may leak into the soil and freshwater.  Smoke and Exhaust: Smokestacks can release various pollutants into the atmosphere along with water and carbon dioxide.  Heat Pollution: Water used to cool factory machinery can runoff into rivers and warm them.