Abstract: A buoyant swimming pool cover is deployable over the surface of a pool under the influence only of the rotation of a power driven roller that extends horizontally across an end of the pool. The roller, which may be of square section, is driven by an electric motor through a flexible drive means including a pulley rotatable with the roller. The roller is rotated to wind the cover onto the underside of the roller. The roller is arranged below the water level of the pool so that upon reversal of the rotation, the buoyancy of the cover will tend to unwind the cover and allow it to be deployed. The square section of the roller provides a number of points at which adjacent layers nip one another to prevent unravelling of the cover as the roller rotates.