An official website of the United States government.

We've made some changes to EPA.gov. If the information you are looking for is not here, you may be able to find it on the EPA Web Archive or the January 19, 2017 Web Snapshot.

Polluted Runoff: Nonpoint Source (NPS) Pollution

Nonpoint Source Pollution Awareness: Darby Duck, the Aquatic Crusader

Darby Duck Overview

Become an Aquatic Crusader and join Darby Duck in the fight against water pollution

What is the Crusaders' weapon? Understanding!

Understanding the characteristics of water, that precious resource we are trying to protect. And understanding how it interacts with other elements in the environment, some of which pollute it and cause problems for people and animals.

How do you become an Aquatic Crusader?

There are seven experiments for you to try that will teach you the characteristics of water. When you complete all seven of the Aquatic Crusader tasks, consider yourself one of Darby's Crusaders too!


Experiment 1: Critter Scope

Did you ever wonder what life is like under water?

Well now is your chance to find out where different insects and their larvae or nymphs live in a stream. The critter scope is an exploring tool that can peek into the lifestyles of the wet and wiggly world.

Materials

  • a can opener
  • a clean coffee can or large juice can
  • waterproof tape or duct tape
  • clear plastic wrap
  • a large and strong rubber band
  • scissors

Procedure

  1. Carefully remove both ends of the can and cover sharp edges with tape.
  2. Place plastic wrap around one end of the can, leaving about one inch extra around the edge.
  3. Put a rubber band around the can and plastic to keep the plastic wrap tight.
  4. Cut excess plastic wrap away and put tape over the rubber band and plastic wrap.
  5. Take your critter scope for a test run in a sink. Look through the open end and place the closed end (the one with the plastic on it) in the water.
  6. Now you are able to visit the wet and wiggly world of a stream.

Note: You might want to try using a clear plastic cover from a fast food salad as a critter scope too!

Experiment 2: Surface Tension

A drop of water is small, but it is made of even smaller parts called molecules. Water molecules have bonds that hold them together. At the surface of the water, the molecules hold on to each other even more tightly because there are no molecules pulling on them from the air above. As the molecules on the surface stick together, they form an invisible "skin" called surface tension.

Water striders and other insects can walk on water without sinking. The surface tension is strong enough to hold them. The insects' feet make dents in the surface tension, but it doesn't break. Here are some experiments to show that surface tension is there, even if you can't see it.

Materials

  • cooking oil
  • water

Procedure

  1. Rub a few drops of cooking oil on your hand.
  2. Let water from a faucet (tap) run over your hand then turn off the faucet. What happens?
  3. Wash your hands with soap. Does this make the oil go away?

How it Works

The water molecules stick together tightly and will not mix with the oil on your hand. Since water molecules are attracted to each other so strongly, they formed small balls or drops which rolled over your oil coated hand. There is an invisible "skin" of surface tension around each drop.

Soap molecules are attracted to both water and oil. One end of the soap molecule sticks to oil, the other end sticks to water. The soap breaks up the surface tension and keeps the oil drops mixed in with the water so that the oil can wash off your hand.

Experiment 3: Shake It Up, Baby!

When you pour two liquids together, will they always mix? Different liquids have different densities, which means that some liquids are heavier than others.

In this experiment, you will see which liquid is heavier: oil or water. You will also learn how detergents work to get greasy, dirty clothes clean.

Materials

  • glass jar with a screw-on lid
  • water
  • cooking oil
  • dish washing detergent

Procedure

  1. In a glass jar, pour one cup of water and a thin layer of cooking oil. What happens?
  2. Screw on the top and shake the bottle to mix the oil and water. Can you get the oil and water to mix together? NO! The two liquids always separate into two layers, no matter how hard or long you shake the bottle. The oil is less dense, or lighter, than the water so it floats on top. Also, the water molecules are more attracted to each other than they are to the oil, so the liquids don't mix.
  3. Next, add a squirt of dish washing detergent to the jar. Put on the lid and shake the jar. Are the oil and water still separated? As the foam clears, you should see a milky liquid and no layers.

How it Works

Detergent molecules are attracted to both water and oil. One end of the detergent molecule loves water and the other end loves oil (and dirt). The detergent breaks up the surface tension that usually keeps water molecules stuck together and allows the water to be free to mix with the oil. This is how detergent and water can get dirty clothes clean.

Experiment 4: Speedboats

Ever wonder how things can move in the water?

Try this!

Materials

  • large, clean bowl of water
  • thin cardboard (index card or notebook cover)
  • scissors
  • liquid dish detergent
  • pencil

Procedure

  1. Draw a triangle on the thin cardboard
  2. Cut out the triangle-shaped boat and float it on the water near the edge of the bowl.
  3. Put a drop of liquid detergent on your fnger.
  4. Gently touch the water behind the boat with your soap covered finger. What happens?
  5. If you want to do this again, you need to get new water that has no detergent in it.

How it Works

The detergent on your finger weakens the surface tension of the water behind the boat. There is still strong surface tension in the front of the boat so the boat is pulled forward.

Experiment 5: Exploding Colors

You can see how quickly detergent molecules start to arrange themselves by doing this experiment:

Materials

  • two colors of food coloring
  • a cereal-sized bowl of milk (skim milk works best)
  • a spoonful of detergent

Procedure

  1. Pour a few drops of each color of food coloring into the milk. Don't stir!
  2. Slowly pour some detergent along the side of the bowl and watch the colors explode.

How It Works

At first, the food coloring rests on top of the milk. The detergent weakens the pull of surface tension in the water where it rains down the side of the bowl. There is still a pull from the molecules on the opposite side of the bowl, so no food coloring is drawn over there. You can try the same experiment using baby powder or pepper instead of food coloring.

Experiment 6: 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.

Materials

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

Procedure

  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.

Extensions

  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.

Experiment 7: No Water Off a Duck's Back

Ducks keep their feathers waterproof by spreading oil from a special gland onto their feathers. However, if excess oil gets into streams, lakes, or oceans, as in an oil tanker spill, it can be harmful to ducks and other water birds.

Oil is one of the most common pollutants in our water. You have probably heard of the Exxon Valdez oil spill. It happened at Prince William Sound in Alaska. Tragedies like this do not happen often, though. Most of the oil in oceans gets there when oil tanks on ships are rinsed while at sea.

When ducks and other waterfowl come in contact with oil floating on top of the water, their feathers become matted. Oily, matted feathers lose their ability to insulate. Because of this, the birds can die from the cold. Also, when the bird tries to clean the oil off of its feathers, it may swallow some of the oil which can lead to stomach ulcers. The only way to save the oil covered birds is to scrub them with detergent, like you might scrub a greasy pan. But this is not a perfect solution. It is very expensive and takes a long time to clean birds.

In this activity you will try several ways to clean up an oil spill. These ways are similar to the ones used by clean-up crews in real life spills. Although oil spills do not happen in all areas, it's good to know how hard it is to clean one up.

Materials

  • one large bowl
  • one measuring cup
  • water
  • cooking oil
  • different dishwashing detergents
  • paper towels or a piece of cloth
  • sponges
  • string

Procedure

  1. Fill half of the bowl with water.
  2. Measure 1/4 cup of oil and pour into the bowl of water.
  3. Gently shake the bowl to create "waves". Did the oil and the water mix?
  4. Now try to clean up the oil using: Paper towel or cloth.
  5. Use string to make a border around the oil and try to drag the oil to one side of the bowl.
  6. Use the sponge to try to soak up the oil.
  7. Try to clean up the oil with each kind of detergent.

Extensions

  1. List five things you can do, starting today, to reduce the number of pollutants you add to the environment.
  2. Take a field trip to a local stream and see if you can find any type of pollution.