This is a typical stream morphology for mid-sized to small streams with a moderate to low gradient: relatively slow-moving pools separated by small "steps" of riffles. I've always assumed the riffles help keep dissolved oxygen levels close to a maximum, but during summer months, the main variable controlling that is water temperature, not aeration.
Photo unmodified. August 30, 2012. FlashEarth Location (completely guessing on this one, but along correct drainage).