Keywords: watershed, erosion, nonpoint, pollution; Grade Levels: fifth through seventh grade; Total Time: two hours plus field trip option; Setting: outdoors (w/ tables)


Students will be able to:

  • Define "watershed," "erosion," and "sedimentation" in terms of the movement of water through a drainage basin (4.1.7.B).
  • Explain the difference between point source and non-point source pollution and give an example of each (4.3.7.B).
  • Explain how non-point source pollution can affect living organisms in a stream (4.6.7.A).
  • Describe how a healthy riparian buffer zone can improve non-point source pollution problems (4.3.7.B).

Materials Needed

Activity 1: Build a Watershed

  • pile of rocks of various sizes and shapes, with sharp angles
  • large, low plastic tubs (such as "under-the-bed" storage units);
  • heavy-duty aluminum foil;
  • mayonnaise, watered-down in plastic squeeze bottles labeled "Rain"
  • Worksheet: "Where Has All the Rainfall Gone?"
  • Salt sprinkler filled with cocoa labeled "Topsoil"
  • Spray bottle of water

Activity 2: It's Not a Nice Sediment

  • cheesecloth squares, 12 inches x 12 inches (enough for two per student)
  • muslin squares, 12 inches x 12 inches (enough for two or more per student)

Activity 3: To Point or Not to Point

Activity 4: Riparian Rain Check

  • four orange traffic cones
  • watch with a second hand;
  • frown flags, 3 inches x 18 inches (one per student)

Assessment Activity


Students will learn about the natural movement of water through a watershed and how human activity can be either detrimental or beneficial to the stream environment.


Activity 1: Build A Watershed

Background: A watershed is the land area from which water drains into a single body of water, such as a stream, river, or ocean. The two largest watersheds in the United States are the Pacific Ocean Watershed and the Atlantic Ocean Watershed, separated by the Continental Divide amidst the Rocky Mountains. A watershed can be as small as the water draining into a puddle in the back yard. Small watersheds generally drain into larger ones, such as a stream progressing from its headwaters at a spring flowing from a mountainside toward a creek, then into a stream, into a river, and finally into the ocean.

  1. Explain to the students that we are going to speed up geologic time, create mountain ranges in minutes, and imitate 40 days and 40 nights worth of rain.
  2. Working in teams of two to four, students will select a number of rocks from the pile and arrange them inside a tub so as to simulate two parallel mountain ranges. They can use the heavy-duty aluminum foil to span the peaks of the rocks, thus making a continuous range of mountains.
  3. When the mountain ranges are completed to the students' satisfaction, give each team a squeeze bottle full of thinned-down mayonnaise. Students should make it "rain" mayonnaise over the topmost ridges of the two mountain ranges. Have them record their observations on Student Worksheet #1: "Where Has All the Rainfall Gone?"
  4. After they have answered the first set of questions, visit each team with a saltshaker full of cocoa. Sprinkle a substantial amount of cocoa on one of the hillsides they have created. Explain that this is where an avalanche occurred, scraping away all the trees and other plants and leaving only loose topsoil.
  5. Have the students complete the worksheet.
  6. Elaborate on the following concepts:
    • When soil is carried over the surface of the earth by water, it is called erosion .
    • Soil that ends up in streams, rivers, and other water bodies is called sediment .
    • Sediment is soil that is no longer in the right place . . . it cannot be used to grow food or forests because it is floating around in the water and sinking to the bottom.
    • Sediment becomes a problem in the streams, rivers, and oceans because it is not supposed to be there.
    • A lot sediment enters water bodies after heavy rainstorms, especially when loose soil is left exposed to the rain.

Activity 2: It's Not a Nice Sediment

Background: Sediment is comprised of soil particles that are suspended in water as a result of erosion. It is a form of nonpoint source pollution that is difficult to control on a societal level. Sediment is harmful to the stream ecosystem because:

    • It makes the water muddy looking and blocks out the light that water plants need to grow. Water plants make oxygen for the water animals to breathe. Without water plants, many water animals also have nothing to eat.
    • Sediment gets clogged up in the gills of fish so they cannot breathe. This would be like human beings trying to breathe in the middle of a dust storm.
    • Fish eggs need to have clean, clear water flowing over them in order to grow and hatch. Water with sediment will smother and kill the eggs. Eventually there will be no more fish.
  1. To demonstrate these problems from the point of view of stream creatures, give each student two squares of cheesecloth and one square of muslin. Explain that they are going to pretend that there has been a big rainstorm. The squares represent different amounts of soil particles that have entered the stream water by being carried along with the rainwater.
    • Ask them what this process is called. (erosion)
    • Ask them what the soil floating in the water is called. (sediment)
  2. It has been drizzling for about an hour. Have the students cover their faces with one square of cheesecloth. They should pretend to be fish (exaggerate opening and closing mouths) breathing through the cloth.
    • Can they see the light as well as before?
    • Can they breathe perfectly well?
  3. Now it has started to rain much harder. The stream is starting to look muddy. Have the students add another cheesecloth square on top of the first square.
    • Can they see the light as well as before?
    • Can they breathe perfectly well?
  4. It has rained very hard all night long now. The stream water is so muddy that you can't see the bottom at all and it looks like chocolate milk. Have the students add the muslin layer to the two cheesecloth layers and try to breathe through it.
    • Can they see the light as well as before?
    • Can they breathe perfectly well?
    • How would it feel if they needed to breathe this way for many days in a row?
    • What if they needed to swim very hard to keep from being washed downstream by the floodwater? (They should imagine running around the block with the muslin over their faces.)
    • If they needed sunlight to grow, would they be growing as fast now?

Activity 3: To Point or Not to Point?

Background: Pollution entering a water body can be classified into two categories. Point source pollution enters a stream (river or other body of water) from a well-defined location, such as an outfall pipe. This source can be traced back to its origination, and the producer of the pollution can be notified so that the problem can be corrected.

Nonpoint source pollution is much more difficult to combat because it involves any pollutant that enters the stream by way of surface runoff. The pollutant might originate anywhere in the watershed, near the stream or miles away. Non-point source pollutants are often substances that are not intrinsically toxic, but if collected in enough concentration they can be detrimental to the ecosystem. Nitrates, phosphates (both needed for plant growth), and soil sediment are examples of these.

  1. Discuss with the students the above background information. Ask them which type of pollution was represented by the loose topsoil (cocoa) on the mountainside during the "Build a Watershed" activity (non-point source).
  2. Demonstrate point source pollution by having a student pour green food-colored water (representing a liquid industrial by-product) through a funnel (representing an outfall pipe) into the stream of one of the tubs used in the first activity. Explain that often the pollution is not intentional, but rather the result of an accident, a system overload, or the failure of part of the manufacturing process.
  3. Assemble the students in a circle. Hand out the "Pollution" cards and have the students place them around their necks so that the words are visible to the group.
  4. Start by naming one of the kinds of pollution showing on a student's card. If it is an example of point source pollution, point to the student with your index finger. If it is nonpoint source pollution, you may not use your finger, but must indicate the student by aiming your bent elbow in their direction.
  5. The student indicated must then (as quickly as possible) choose another student, call out his or her example of pollution, and "point or non-point" to them.
  6. The game continues, faster and faster, becoming hectic and humorous. If a student accidentally points "illegally," they must step out of the circle. The circle thus becomes smaller and smaller until only a few students are left.

Activity 4: Riparian Rain Check

Background: The riparian zone is the land adjacent to a stream or river. A healthy, functioning riparian zone is characterized by a diversity of plants, including trees, understory, and herbaceous species. The presence of a wide riparian zone ensures a healthy stream ecosystem in a number of ways and is the best method known for reducing the threat of non-point source pollution.

    • The widespread roots of the trees, warm-weather grasses and other herbaceous plants help to hold the soil in place, especially along the banks of the stream.
    • Leaves and branches of the plants (of all sizes) break the force of falling raindrops, reducing the energy of the moving water. Slower-moving water is less likely to dislodge and carry soil particles into the stream.
    • Trees in the riparian zone absorb excessive nutrients, such as nitrates and phosphates, which may have been carried with rainwater from farmers' fields or residential lawns. These nutrients become bound in the growth of the tree and are held "in storage" until such time as leaves and branches fall to the ground or into the stream. There, with the help of decomposers, the nutrients are slowly released and recycled into the system through the food chain.
    • The survival needs for many wildlife species (food, water, shelter and space) are provided in a diverse, well-vegetated riparian zone.
  1. Discuss with the students the above-listed functions of a riparian buffer zone. If possible, bring the group to the edge of an established riparian buffer to show them concrete examples as you direct the discussion. Compare this with an area without a buffer.
  2. Set up for the "Riparian Rain Check" game. Place two orange traffic cones approximately 15 feet apart on a playing field (these represent the edge of the stream). Place another two cones about 25 feet apart, located approximately 30 feet down the field from the first set (these represent a construction site with loose topsoil and no erosion control devices).
    • Construction Site
      • 25 feet apart *
      • 15 feet apart *
      • Stream
  3. Tell the students that they are going to become a newly planted riparian buffer zone on a rainy day. Select two students to be tree seedlings. They will station themselves somewhere near the stream bank, between the two cones. Their job will be to stop the raindrops before they can carry non-point source pollution into the stream. The remaining students will be raindrops carrying sediment toward the stream. Give each of these students a brown flag to tuck into their clothing and mark them as raindrops/soil particles.
  4. The raindrops/soil particles should line up at the construction site. When the leader yells, "Go!" the raindrops should run toward the stream bank and attempt to cross the line (they must run between the cones). The trees should attempt to tag as many raindrops as possible keeping one foot "planted" in the ground at all times. When they capture a raindrop, the trees should take their brown flags. Time this "rainstorm" for 10 seconds (adjust time according to the group's age and ability). Yell, "Stop!" when the time is up.
  5. Count and record the number of raindrops that were intercepted by the trees during the 5-second time period. Explain that the nutrients carried by the raindrops has been captured by the root systems of the trees, and now it has been used to help the trees to grow and reproduce. The students who were tagged will now become trees (as the riparian zone grows wider and more vegetated).
  6. Repeat the exercise with the additional trees guarding the stream. Count the captured raindrops again. Were there more captures? (Just as more non-point source pollutants can be filtered out by wider and more vegetated riparian buffer zones.)
  7. Variation: have the trees link arms and stand directly in front of the stream bank to protect it. This simulates the intertwining of roots in the stream bank. The trees may decide to test whether it is more effective to be planted next to the stream or further away. Discuss the results.
  8. At the conclusion of the game, explain that the riparian buffer zone acts to filter out non-point source pollutants such as sediment. The wider and more vegetated the buffer, the more effective it is.
  9. Ask the students to describe ways that human activity can change the condition of the stream. Be sure that positive (plant riparian buffer zones) as well as detrimental (over fertilizing lawns, disturbing soil, and leaving unprotected) activities are mentioned.

Assessment Activity

  1. Walk alongside a stream that has a well-vegetated, wide riparian buffer zone.
  2. Have the students point out examples of healthy riparian zone components: habitat for animals; roots on trees that are holding together stream banks; native grasses with deep root systems to absorb runoff, capture erosion, and absorb excessive nutrients and other pollutants; trees that are cooling the water by leaning over the stream; trees and other plants that have fallen into the water to provide food for the water creatures, etc.
  3. Ask the students to imagine the area during a heavy thunderstorm. Then ask the following questions to test and reinforce their knowledge:
    • From which direction would the water come? (uphill)
      • What is the word that describes the land that drains into this stream? (watershed).
    • When water dislodges loose soil and sweeps it into the stream it is called "___." (erosion)
    • After the soil enters the stream, that soil is called "_____." (sediment)
      • Why would sediment be a problem? (Clog fish gills, block sunlight, smother eggs and other aquatic life).
    • Would we consider that to be a pollutant? (yes) Why? (It is too much of a good thing, located in the wrong place to be useful.) * What classification of pollutant would the sediment be? (non-point source)
  4. Review and reinforce the concepts by playing a "Reinforcement Relay" game.
    • Set up four shoe boxes, labeled with "Food," "Filter," "Nutrient storage," and "Habitat."
  • Divide the group into two equal teams.
  • Give each student a scenario card. Allow several minutes for students to read the cards.
  • At the signal, the first team player in each line will run to the shoebox that is labeled with the riparian zone function that matches the scenario on his card. After depositing the card in the appropriate box, they will return to tag the next person in line.
  • After all the cards have been deposited, empty one shoebox at a time, read each card out loud and discuss with the group. If a mistake was made, simply discuss the correct answer, but keep the mistake-maker anonymous.


Welsch, David J. (1991). Riparian Forest Buffers: Function and Design for Protection and Enhancement of Water Resources. Radnor, Pa.: USDA Forest Service.

Wildlands Conservancy. Non-point Source Pollution: The Quiet Threat to Our Streams. Emmaus, Pa.


Barbara Morton, Wildlands Conservancy, Emmaus, PA