A fluid diversion conduit is described for diverting the flow of fluid, and particularly for diverting water from a stream to a discharge location. The discharge end of the duct has a segment of gradually enlarging cross sectional area, forming a hydraulic flow diffuser. Water flow through this segment is thereby slowed as the flow area increases, and most of the dynamic head of the water flow is recovered, improving flow capacity of the conduit. The rate of flow through the conduit may be monitored and controlled to achieve streamline flow in the diffuser section, and to prevent air from entering the diffuser section. Air entering the conduit may be expelled or otherwise displaced from the conduit.