A system for cooling the temperature of a body of water having a top surface exposed to sunlight comprises hydrophilic balls distributed on, and in direct contact with, at least part of the top surface characterized prior to the distribution by a pre-distribution surface area. The balls have diameters within a range of 100 microns to 3 mm, and albedos within a range of 0.15-1.0. The balls comprise recycled glass and air-entrapping pores. The hydrophilic surfaces of the balls provide a total wetted surface area after the distribution greater than the pre-distribution surface area of the water, facilitating the cooling.