Water districts in Southern California are using so-called "shade balls" to protect their water supplies, turning them into what looks like giant ball pits.

These 4-inch diameter balls are hollow and filled with water as ballast to prevent them from blowing away in the wind. The black spheres, floating on the surface of the water, shade the pond below to prevent bromate, a hazardous chemical that forms when a disinfectant in the water undergoes a chemical reaction triggered by sunlight.

In 2013, the L.A. Department of Water and Power ordered 6.4 million shade balls for use in area reservoirs. According to the company that manufactures them, the shade balls reduce water evaporation by as much as 90 percent.

Oh, and did we mention that watching them roll across the water is really fun? See them being unleashed upon a reservoir in L.A.:

Also called bird balls, these opaque plastic balls are also often used to deter birds from hanging out at ponds near airfields.

All hail shade balls.

[h/t: Vox]