In this activity, learners model estuaries, artificially enriching both fresh and salt water samples with different amounts of nutrients and observing the growth of algae over several weeks. Learners relate their results to the phenomenon of algae blooms in estuaries. Learners then analyze data for different sites at the Guana Tolomato Matanzas National Estuarine Research Reserve (GTMNERR) in Florida to discover the relationships between nitrogen, chlorophyll, and dissolved oxygen. Finally, learners study how nutrients cycle through an estuary and suggest recommendations for reducing nutrient inputs to estuary waters.