Lesson Plan

Title of lesson: THE GREAT SALT WEDGE!

Topic: Unique properties of estuary environments

Grade level/s: 10-12th grade

Time needed: One 45 minute period

Science background material for the teacher:

Saltwater is denser than freshwater.

A salt wedge forms at the boundary between freshwater such as a river, and the ocean.

The wedge shape is a result of the denser saltwater diving below the freshwater, and the constant opposing current from both bodies of water.

This boundary forms a unique ecosystem known as an estuary.

Instructional Objectives:

SWBAT describe the differences in density between fresh and saltwater.

SWBAT compare and contrast the environment at an estuary with that of a marine or freshwater environment.

SWBAT define a salt wedge.

National Science Education Standards :

Content Standard A: Science as Inquiry

* Abilities necessary to do scientific inquiry

* Understandings about scientific inquiry

Content Standard C: Life Science

* Interdependence of organisms

* Matter, energy, and organization in living systems

Content Standard D: Earth and Space Science

* Geochemical cycles




Food coloring (two colors)


Digital Projector and Laptop




Advance organizer:

Students will construct a Venn Diagram using their prior knowledge of the differences between fresh and saltwater. The Venn Diagram will compare and contrast properties of fresh and salt water.


Students will begin the lesson by using their prior knowledge to complete the Venn Diagram comparing fresh and saltwater properties.

Teacher then instructs students to form groups of two, and brainstorm some ideas about what happens when fresh and saltwater come in contact with each other. Students will be provided with different colored water in jars to represent the two types of water. They will be instructed with their partner to combine the two colored waters, and record the results in their notes.

Teacher will then ask the class a question. “What is a salt wedge?” Student must answer the question in their notes. They will be give a minute to do this.


The video ends with a clear image of a saltwater wedge formed on the bottom of the demo tank. If the video is projected on a SmartBoard you can outline the wedge with a marker and ask student to re-evaluate their previous answer.

Define salt wedge on the board, and have students copy the definition into their notes.

Ask students to compare the results they got when they mixed their own water, with the results shown on the video. How were they different? What can you conclude about large bodies of water that you cannot conclude from mixing the two kinds of water in a cup?

Explain to students that this is exactly what happens when a river empties into an ocean. This unique ecosystem where fresh and saltwater meet is known as an estuary.

Exit Quiz: Have students write on a slip of paper some suggestions for unique adaptations animals and plants could have to living in an estuary environment.

Adaptations for students with disabilities:

Subtitles on the video could be an option for the hearing impaired.

Multicultural Connections:

Ask students if any of their families live nearby a body of water, such as a lake or an ocean. What unique animals and plants live along those bodies of water?

Possible ways technology might be incorporated:

Instead of having students mix the waters themselves, you could use an animation or video of a cup of saltwater and freshwater mixing together in a container. Further expansion might include a smartboard interactive animation that does the same thing.