Device (5) and method or removing suspended-material particles, more particularly fine and ultra-fine particles from a water flow containing suspended-material particles in a pressurised water line (3) of a hydroelectric power plant (2), whereby a tubular element (6) forming a flow channel (7) is provided in the pressurised water line (3), whereby the flow channel (7) essentially extends in the axial direction of the pressurised water line (3), and in the flow channel (7) a stationary swirl-generating device (11) is arranged for stimulating a flow component of the water flow which runs perpendicularly to the main flow direction (9), and in the flow direction after swirl-generating device (11) a separating device (13) is provided for removing the suspended-material particles carried radially outwards due to the effect of centrifugal force.