As you visit your river keep an eye on the river bottom and determine whether or not it would be a good place for trout or salmon to lay their eggs. Remember that the trout lay their eggs in the spaces between the gravel of the stream bed. But if the river has too much fine sediment, like sand or clay, these spaces will become filled and the fish can't lay their eggs. When the spaces in the gravel have been filled in, fisheries biologists say that the gravel and bottom rocks are "embedded".
Your teacher can discuss with you how much embeddedness the trout can tolerate and can show you how to measure embeddedness so that you can report areas of the river where there are too many sediments.