a portable spa including a cover having two semi - circular , rigidly molded , interlocking halves , designed to conform with the contour of the rim of the spa . the cover halves each have an undersurface and outer surface with a plurality of radial support ribs being formed in the undersurface to provide strength and rigidity . elongated , tapered male and female hinge members are integrally molded as part of the respective cover halves and permit the cover halves to be engaged and disengaged from one another when at an angle with respect to each other , while remaining firmly locked together when each half lies horizontally . the horizontal engagement is further facilitated by resilient fingers which extend out from the male projection at intervals along the cover edge and provide a resiliently biased interlocking mechanism .