Abstract: The disclosure is of a buoyant, air-filled, plastic cover for swimming pools, large ponds, and the like, and to facilities by which these may be constrained to float on the water (or other liquid) without proneness to disarrangement, especially in the regions of skimmers formed in the sides of the pool.There is disclosed a pool cover subdivided into interfitting sub-sections, preferably of a rectangular shape. These are provided with coacting marginal abutments which interengage to prevent one cover section from overriding another. These abutments are in some cases of sufficient specific gravity to sink the edge portions of the cover sections somewhat deeper in the water than the remainder of the cover, which is airfilled, and of low specific gravity. Abutting, or interengaging edge elements are disclosed which mechanically engage in a confining manner, preventing overriding.