A pump casing for a centrifugal pump, which comprises an inlet opening, a discharge outlet, and a transition surface extending between an inner peripheral surface of the main pumping chamber and an inner peripheral surface of the discharge outlet, the transition surface arranged for separating an in use exit flow of material in the discharge outlet from an in use recircula tion flow of material in the main pumping chamber. The transition surface has a cutwater having a profiled section which comprises a protrusion which extends irregularly from an otherwise generally rounded arched or U-shaped transition surface and is configured such that, in use, the velocity and/or turbulence resulting from the in use flow of the material being pumped in the main pumping chamber is reduced.