Here’s a simple activity that you can use to show your students one way that freshwater and salt water differ. You will need a large glass or clear plastic container, water, a few tablespoons of salt, a spoon, and an egg.

Fill the glass with water. Carefully place an egg in the water and allow your students to watch what happens. The egg will sink to the bottom of the glass. Empty the glass and then refill it with water. Now add a few tablespoons of salt to the water and stir to dissolve some of the salt. Ask students what they think will happen when you place an egg in the glass. Put the egg in the saltwater and allow your students to watch. The egg will now float in the water. This happens because salt water is denser than freshwater. For the same reason, it is easier for a person to float in the ocean than in a lake!