Read books, magazine articles and studies from credible conservation organizations. Gather data on the flora, fauna, wildlife and food webs within a freshwater ecosystem. Identify a nearby freshwater habitat that you would like to study. Visit the site and take a survey of any problems you observe, such as pollution or clear cutting. Speak with a wildlife conservation officer about other problems in the area, such as dropping wildlife populations, invasive species or plant diseases, which may not be obvious to the untrained eye. Choose one issue to focus on, and pose a question such as, "How does water pollution affect biodiversity in a freshwater ecosystem?"
Using the knowledge you have gathered from your research, come up with a hypothesis to help answer the question chosen. For example, "More types of wildlife live near a clean body of water than a polluted one." State your hypothesis in terms that can be easily measured.
Observe biodiversity in your chosen area by conducting wildlife surveys over a period of time. Take pictures of your observations. Take water samples and test for contaminants and microscopic life. Compare the biodiversity between a relatively clean body of water and a polluted one. Work with an environmental organization to clean up a polluted area and compare biodiversity before and after several months of conservation work to see if you are making a difference.
Write a summary of your research, hypothesis and testing activities. Create graphs and charts to provide a visual representation of the measurements you took during water pollution and biodiversity testing. Arrange the reports and graphics neatly in chronological order on a tri-fold display board for presentation at a science fair.