Stream reach metabolism integrates organism respiration & production to provide a valuable ecosystem measure that varies as a function of biotic & abiotic factors. As a powerful indicator of whole system functioning, it is important students can estimate stream metabolism. This field lesson engages students in study of ecosystem metabolism through its components, production & respiration. Students connect to the reach through guided reflection, predict and explore dissolved oxygen, investigate metabolism drivers in a matching game of diel oxygen curves from streams around the world, and collect & analyze diel dissolved oxygen data. This is designed for mid to upper-level undergraduates to complete in one 2-hour field visit at a wadable reach of run habitat, and a 30-minute analysis session. This lesson complements lessons including hydrogeomorphology, field sketching, organismal studies, ecosystem energetics, mapping, any that provide an ecosystem or energetic framework (RCC, Fluvial Landscape Ecology) to student understanding of flowing waters. Additionally, it can be replicated in space and time to highlight the relative importance of the key drivers of ecosystem metabolism.