Apparatus for covering a liquid basin, such as a swimming pool. The apparatus comprises a roller-blind type cover assembled from hollow slats arranged to be spread over the surface of the liquid. According to the invention the cover is constructed so as to be stackable accordion-wise by the side of a shaft or roller with which the cover is spread over the surface of the liquid or withdrawn from it, thereby to reduce weight on said shaft or roller compared with a prior construction in which the cover is wound upon the shaft.
