Abstract: A cover assembly for a swimming pool is provided for winter protection of the pool and the water contained therein. The assembly includes a cover and an adjustable ring assembly for securing the cover against the inner side of the pool's peripheral wall. The ring assembly may be of one-piece construction or may be multiply-segmented. In either embodiment a ring size linear adjusting assembly is provided to firmly position the ring assembly to the inner side of the peripheral wall. The adjusting assembly may either comprise a pair of adjustably interlocking segments or a ratchet mechanism.