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Over 90 million 4-inch-diameter plastic balls, called shade balls, cover the Los Angeles Reservoir to block sunlight from penetrating the 175-acre surface of the reservoir, preventing chemical reactions that can cause algae blooms and other problems, Los Angeles, California, August 12, 2015 (Credit: AP Photo/Damian Dovarganes)

Over 90 million 4-inch-diameter plastic balls, called shade balls, cover the Los Angeles Reservoir to block sunlight from penetrating the 175-acre surface of the reservoir, preventing chemical reactions that can cause algae blooms and other problems, Los Angeles, California, August 12, 2015 (Credit: AP Photo/Damian Dovarganes)