Abstract: A method and system for collecting fluid samples from a high velocity effluent comprises a pump which is periodically energized to draw the fluid through a sample chamber and into a collection container. The sample chamber comprises four valves which are operated automatically in response to negative hydraulic pressure generated by the pump, viz: an inlet valve for receiving fluid from the sampling point, a first outlet valve connected to the pump, a second outlet valve for draining the fluid samples to the collection container and an air release valve. During a sampling cycle, with the pump energized, fluid is drawn from the sampling point at a velocity greater than or equal to that of the effluent. The fluid is directed through the inlet and first outlet valves of the sample chamber and to a reservoir. At the end of the sampling cycle, with the pump de-energized, a fixed volume of the fluid remaining in the sample chamber is drained into the collection container through the second outlet valve.