Laboratory experiments were conducted to investigate the effect of fluid motion on the growth and metabolism of the freshwater periphyton Spirogyra and Stigeocloniom. The only growth-limiting factor was the effect of fluid motion; all the other environmental conditions, such as light, temperature, and nutrients were not limiting growth. The growth rates of periphyton were measured in terms of the chlorophyll-a concentration, and the metabolism was characterized by dissolved oxygen concentration measurements. The periphyton growth and corresponding photosynthetic rates were the lowest in a stagnant fluid. In a moving fluid the periphyton growth was mediated by the fluid flow conditions at the channel bottom. The results indicate critical conditions, corresponding to the detachment of periphyton in the channel bed. A functional dependence between the periphyton detachment and fluid flow conditions is proposed.