Build Your Own Watershed

A watershed is an area of land where all the water from rainfall, streams and rivers drain to a common outlet like reservoirs, bays or larger rivers. It is the ecosystem in which we all live including the wildlife, surface waters and, of course, our neighborhoods. Sometimes, the word watershed is used synonymously with drainage basin or catchment. In San Diego County, we have a total of eleven watersheds.

Try this experiment: build your own watershed at home and explore how water flows across the land.

San Diego Watersheds

You will need the following:

  • 1 large tupperware container or roasting pan
  • Scrap paper or newspaper
  • Rocks of various sizes
  • White trash bag
  • Cup of cocoa mix, iced tea mix, or other flavored drink mix (to represent chemicals)
  • 1 spray bottle filled with blue-colored water


  1. Use the paper and rocks to make an uneven surface in you container. You are constructing the topography of your watershed.
  2. Cover your topography with the white trash bag; be sure to tuck in the edges under the rocks. It might be helpful to use some rocks to hold the trash bag in place.
  3. Spray your watershed with the blue-colored water to simulate precipitation. Where does the water in the watershed flow?
  4. Sprinkle the cocoa mix over part of your model. The cocoa mix represents chemical runoff that is polluting the watershed. Spray the model again and watch how the contaminated water travels through the watershed.



Follow-up Questions:

  1. What are some things that can pollute our watershed?
  2. How can we reduce the impact that we have on the watershed and the environment?

Did you build your own watershed? We want to see! Send us a picture at [email protected] and be featured on our blog.

Are you a teacher who wants to use environmental education lessons in your classroom? Checkout Project SWELL: a school-based science curriculum that teaches children about the importance of the San Diego region’s waterways. Project SWELL helps teachers empower students about how to understand and improve the condition of San Diego waterways. For more information go to

Photo credit: Shannon Switzer