A system for maintaining and/or cooling the temperature of a body of water exposed to sunlight comprises hydrophilic balls distributed on the surface of the water. The balls have diameters within a range of about 0.015-3.0 mm, and albedos within a range of about 0.15-1.0. The surfaces of the balls provide a total wetted surface area greater than the pre-distribution surface area of the water. In one embodiment, the body of water may be a natural or unnatural lake or bay.
