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Polluted Runoff: Nonpoint Source Pollution

Darby Duck, the Aquatic Crusader - Sink or Swim?

Sometimes detergents get into creeks or lakes. This could happen if people use too much soap to wash their cars. Then the water washes down the street into street drains and into a creek or lake. Once in the creek or lake, detergent could destroy the surface habitat.


  • a clean bowl (free of detergent)
  • paper clip or sewing needle
  • fork or tweezers
  • liquid dish detergent


  1. Fill the bowl with water.
  2. Put a paper clip or needle on the times of the fork, or hold it with the tweezers. Gently place the paper clip or needle on the surface of the water. Be patient and careful. You will be able to get the clip to sit on top of the water! Can you see the surface tension bend under the paper clip?
  3. Add one or two drops of detergent to the water near (not on top of) the paper clip. What happens?

How it Works

The paper clip was resting on top of the surface tension. This "skin" supported the clip and kept it from sinking. When you added detergent, the soap weakened the attraction the water molecules had for each other. This caused the surface film to disappear. Then the paper clip sank.


  1. Keep your eyes open and report any drastic changes in your stream.
  2. Organize watch groups.
  3. Make it a habit to carry a trash bag with you when you go out to a lake or stream. detergent