Salish Sea Geography and Tides- A Web Search!
  • This lesson plan is also available in PDF Click here to download
  • This lesson should follow a lesson on tides.
  • Created for students 4th-6th grade
  • Supplement for the following FOSS Kits: Water, Environments, Landforms and Structures of Life
  • Lesson takes approximately 2 to 3 class sessions (35-45 minutes) or one long class session (1-2 hours)
  • Uses science notebooks
Big Ideas
  • The Salish Sea has a large watershed extending from Olympia, Washington north to Campbell River on Vancouver Island, Canada. The Washington part of the watershed is generally called the Puget Sound, the Canadian part is called the Georgia Basin.
  • The Puget Sound, Georgia Basin and entire Salish Sea are estuaries.
  • Tides within the Puget Sound and Georgia Basin differ from those along the Washington and Canadian Coasts.
Essential Questions
  • What factors cause tides within the Puget Sound and Georgia Basin to differ from those along the coast?
  • How do tides within the Puget Sound and Georgia Basin differ from those along the coast?
GLE Ties

Science 2.1.3 Explaining
Apply understanding of how to construct a scientific explanation using evidence and inferential logic. W
Reading 2.3.2. Understanding Meaning

Analyze sources for information appropriate to a specific topic or for a specific purpose.

Salish Sea Watershed Estuary
Puget Sound Georgia Basin Fresh water


Possible Misconceptions
  • Students make think tides are caused by waves.
  • Students may not be familiar with Salish Sea geography, and thus assume that the water salinity and tides of the Puget Sound and Georgia Basin are the same as the open ocean.
Instructional Strategies
  • Direct instruction
  • Using maps to draw conclusions
  • Internet research
  • Group discussion
  • Check for understanding in science notebooks, on worksheets, and in discussion.
  • Check the students "exit ticket" answers to make sure that they get the "big ideas" from the lesson.
System Description

This lesson focuses on the Puget Sound Estuary Tide System.

The important structures are:

  • Oceans, bays, inlets, rivers that feed into the Puget Sound
  • Puget Sound geology

Matter and Energy Transfers :

  • Motion of one body of water transfers to another

Forces acting on the system:

  • Landforms blocking and/or redirecting water flowing into and out of the Puget Sound






Lesson Description













Lesson Description
















Lesson Description

Per Student:


  1. Tell students that today they will be learning about the body of salt water that we live next to: the Puget Sound. We'll be exploring how its special geography makes its tides different from those on the Washington coast.

  2. Pass out the map of the Salish Sea to each student. Explain that, despite being in two different countries, the Georgia Basin and Puget Sound are actually one large body of water, which is sometimes called the Salish Sea (the Salish Sea watershed is outlined in red on the map). For this lesson we will be focusing on Puget Sound (the area below the red dotted line on the Salish Sea map).

  3. Have students write a list in their science notebooks of all the water sources they think feed into the Puget Sound.

  4. Conduct a short discussion where students share the ideas they wrote down. You could record these ideas on a white board or piece of butcher paper. In addition to rivers and streams, you should point out that sources such as farm run-off, parking lot run-off, storm drains, and leaking septic tanks also drain into Puget Sound. All of the land that drains fresh water (although it is called fresh water, that doesn't mean it's always clean) into a body of water is called a watershed. Puget Sound, the Georgia Basin and the Salish sea all have watersheds, even though they are different sizes. Explain that there can also be smaller watersheds within large watersheds. It is all a matter of scale. For instance, the watershed of the Skagit River in Skagit County is within and smaller than the watershed of the Puget Sound.

  5. Explain that the Puget Sound, Georgia Basin and Salish Sea are estuaries. Estuaries are "semi-enclosed coastal bodies of water which have a free connection with the open sea and within which sea water is measurably diluted with fresh water derived from land drainage" (Cameron and Pritchard, 1963). In short, a partially enclosed body of water where fresh and salt water mix. Refer to the Salish Sea map to show how estuaries in the Salish Sea are partially enclosed by land. Also point out the sources of salt water and fresh water. *Explain that the Salish Sea gets over half its fresh water from Canada's Fraser River.


  6. Review what causes tides (primarily, the moon and sun's gravitational pull combined with the earth's centrifugal force). Students should have completed a lesson on tides prior to this lesson. More on tides:

  7. Explain to students that the Puget Sound tides are unique from those that occur out on the Washington Coast. Explain that, although the Puget Sound is not too far from the Washington coast, tides are very different in the two areas. There are much larger fluctuations between high tides and low tides in the Puget Sound than on the Washington coast.

  8. Tell students that they will be working on-line to better understand why tides within the Puget Sound are so unique.

  9. Pass out the worksheet. Tell students that they must first answer question one before they go on to the web-search.

  10. Have students work independently, or in groups of up to three, on the Web-Search.


  11. After students have completed the worksheet, go through the answers for the web-search together (see end of document). Encourage students to fix mistakes so they can use their work as a reliable reference. It would be helpful to be able to refer to the Salish Sea map as explanations are being given, especially on questions 2, 4, and 5.

  12. Ask students why they think the Puget Sound tides occur at different times at different locations. Explain that this happens because the water from the Pacific Ocean must travel around many landforms, both above and below sea level, which slows the water down. For example, places such as the Tacoma Narrows are very narrow, causing the water that moves through it to take longer compared to when the same volume of water moves through wider areas in the Puget Sound. It also takes a longer time for water to travel long distances from the source to the most southern and most northern tips of the sea regardless of obstacles.

  13. Next, ask the students why they think the tides are more extreme in Olympia than at Port Townsend (or more extreme in the South Puget Sound versus the Strait of Juan de Fuca). Explain that during high tide, the water up north (near Bellingham and Port Angeles) has room to spread out and continue moving, whereas down in Olympia the water is being pushed into a narrow space and eventually hits the land at the bottom of the Puget Sound, causing the water to build up higher. During low tide, the water moving out of the South Puget Sound area is moving north into deeper water and spreading out into the estuary, while also not being refilled.  This causes low tide to be very low. In the North Puget Sound, the low tide is not as extreme because as the low tide is pulling the water from the North Puget Sound out through the Strait of Juan de Fuca, it is also pulling the water from the South Puget Sound into the North (effectively replacing some of the water that drained out).  The opposite effect would happen in the Georgia Basin: since the water there moves south towards the Strait of Juan de Fuca during low tide, the northern part of the basin would have more extreme low tides. The middle part of the Salish Sea, closest to the Strait of Juan de Fuca, would have the least extreme tidal patterns because the water has a shorter distance to travel and there are not as many obstacles in the way.

  14. Have students answer the following "exit ticket" questions in their science notebooks so you can check for understanding before they move onto the next subject activity.
    • Are tides more extreme (higher highs and lowers lows) in the North or South Salish Sea?
    • Why are the tides more extreme in some areas than others?

Web-Search Answers
  1. Anwers will vary
  2. "...Variations in depth and width, topology of the Sound, and the gravitational pull of the Sun and Moon and other gravitational influences.
  3. a-450 feet, b-930 feet, c-just north of Seattle
  4. aait of Juan De Fuca, b-Olympia
  5. see step 13 under "summary" in procedures section