Numerous studies have shown that low flow condition is the main trigger of algae bloom and flow management is widely acknowledged as a strategy for inhibiting bloom development based on critical flow velocity and replacement.Due to the underlying intervention mechanism is still not clear, long-term practices of flow management are not very effective. Based on the research progress and a series of studies through long-term observation, enclosure and laboratory experiments, we present the conceptual mechanism that there existed three different mechanisms of hydrodynamic impacts on freshwater algae:(1) low turbulent flow results in the thickness of cell diffuse layer thinner in favor of nutrients transport from water phase to algae cell,which is preferred by algae growth; (2) medium turbulent flow is harmful to nutrients absorption and light availability of algae and inhibits the algae growth; (3) high shear force can damage the algae cell walls, which are individually determinant in different levels of flow intensity. According to theories, critical flow velocity should be applied from two different aspects of water replacement and cytology in flow management. The results will be of great scientific significance in order to control algle bloom and remain the water quality in flow management.