“Shade balls”, there are 96M of them in (on?) a big Los Angeles reservoir : https://en.wikipedia.org/wiki/Shade_balls https://en.wikipedia.org/wiki/Shade_balls

“Shade balls”, there are 96M of them in (on?) a big Los Angeles reservoir : https://en.wikipedia.org/wiki/Shade_balls https://en.wikipedia.org/wiki/Shade_balls They are made from HDPE, with an additive to prevent UV-accelerated breakdown into bromates (which is what they are there to stop forming in the water, as well as to stop evaporation).