Working with the K’ómoks Nation towards Q’waq’wala7owkw on their unceded territory.

Working with the K’ómoks Nation towards Q’waq’wala7owkw on their unceded territory.


Suggested Grades: 4-6

Driving Questions

  • What is a saltwater wedge?
  • Why does freshwater stay at the surface while salt water will travel up a river along the bottom in a wedge (because of density differences)?
  • What are the water characteristics of an estuary, (from salty ocean water, to brackish, to fresh).
  • How are animals and plants affected by a saltwater wedge in an estuary?

Learning Intentions

  • I am aware of how salt and fresh water interact in an estuary
  • I can share/teach this idea with others


Special Note:
To mix a seawater solution, add 35 grams of kosher salt (regular salt has additives) to 1 liter of water or approximately 1.2 ounces (2 scant tablespoons) of salt to 1 quart of water. To make a brackish mixture, halve the amount of salt Tint the fresh water and the salt water volumes with the food coloring before adding them to the tote.

Curricular Competencies


  • Questioning and predicting
  • Planning and conducting
  • Processing and analyzing data and information
  • Evaluating
  • Communicating


  • Communicating and representing
  • Reasoning and analyzing


  1. Place one end of the box or tote on a small block  Place a piece of white paper under the box and fold the extra paper up along the back to produce a white background.
  2. Make several tiny holes in the bottom of the cup. Weight the cup with small stones and place at the lower end of the tote.
  3. Pour cool, fresh water (hint: tint it with yellow food colour)  into the tote until it reaches close to the top of the cup. Allow the water to settle.
  4. Gently pour the cool, salty, red-tinted water into the cup (do not overfill).
  5. Describe what happens.  (see photo below)
  6. Why?


Estuaries are extremely valuable and productive areas. Research and report on why they are so valuable and what sorts of resources are found there.

  1. Take a field trip to an estuary. Test water samples from various parts of the estuary with a commercial hydrometer which measures salinity (the saltier the water the more dense it is and the higher the reading on the apparatus) .

Saltwater wedge demonstration: red water is saltwater (bottom) and yellow is the freshwater (top)


Click here to download a printable version of this lesson

This lessons pairs well with the Water Sampling Lesson.

Community Connection

This lessons is often part of a Down by the Bay Field Trip. Project Watershed can supply the materials for this lesson. Contact Project Watershed to arrange a field trip or the delivery of materials.