This two-part lesson is a hands on representation of the distribution of fresh and salt water as it occurs in an estuary. Students observe the layering effect when the different densities of salt and fresh water meet. Organisms are introduced into the simulated estuaries and students observe their behavior and interactions.

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1. Anadromous organisms such as salmonids must deal with density changes due to salinity content as they change their habitat requirements throughout their life cycle.