An invented hinge for coupling three buoyant-slats pool cover sections together is described wherein three, modified, longitudinal buoyant slats are coupled for pivoting around three angularly spaced, parallel hinge axes aligned with the slats by a plurality of hinge plates each defining a coupling aperture received and pinned within registering hinge bays penetrating into adjacently positioned, longitudinal side flotation chambers of the three modified buoyant slats by a longitudinal hinge pin passing through the coupling apertures of the hinge plates received in the hinge bays inside of the flotation chamber of each of the three modified, buoyant slats. The three modified longitudinal buoyant slats of the assembled hinge present three cooperating coupling structures extending longitudinally along the slat sides opposite the pivot axes of the hinge for coupling a vertical section and two horizontal sections of a buoyant-slat pool cover extending/retracting from an interior, pool bottom cover drum trough where the vertical section extends up and down between the cover drum and the pool surface and the horizontal sections coupled to the end of the vertical section extend/retract in opposite directions across a pool surface.