According to a recent Ripley’s Believe It Or Not newspaper feature panel, “Thousands of black plastic balls float atop the 58-million-gallon Ivanhoe Reservoir in Los Angeles, Calif., to provide shade for the water and to prevent carcinogens from forming!” Hoping to at least find a better picture than their typical hand sketch version, I thought I’d look it up.
The Los Angeles Times covers the incident, where the Department of Water and Power there dropped 400,000 large black plastic balls. More like rolled, perhaps.
As is typical RBION style, the hand-drawn illustration is actually a re-creation of an actual photograph, this one, and here are a few others. This article has a picture of the approximate size of one of them, as held in the hand. And still, yet more pictures.
The idea in doing so, was to prevent chlorine (cleansing agent), bromide (naturally found in groundwater) and sunlight mixing to create a poisonous combination — by mostly eliminating the effects of sunlight on the water. Looks cool, at least.