I took a boat through 96 million black plastic balls on the Los Angeles reservoir to find out why they're there. The first time I heard about shade balls the claim was they reduce evaporation. But it turns out this isn't the reason they were introduced. Huge thanks to LADWP for arranging this special tour for me. Next time let's put the GoPro on the submersible! The balls are made of high density polyethylene (HDPE) which is less dense than water so they float on the surface of the reservoir even if they break apart. They are 10cm (4 inches)...