They're hypnotic and incredibly odd. Thousands of black plastic "shade balls" were released this week into the Los Angeles Reservoir to float and bob on the surface, looking like a kind of dark playground ball pit.

The release of this batch of 20,000 balls into the 175-acre reservoir was the culmination of a $34.5 million initiative to protect the water supply that involved the deployment of a whopping 96 million plastic balls into the water.

“In the midst of California’s historic drought, it takes bold ingenuity to maximize my goals for water conservation,” said Los Angeles Mayor Eric Garcetti, who helped release the balls. “This effort by LADWP is emblematic of the kind of the creative thinking we need to meet those challenges."

The balls are intended to prevent sunlight-triggered chemical reactions that encourage algae — creating cleaner water, says Garcetti. The bobbing balls also protect the water from wildlife. But the key benefit is that the floating ball will prevent evaporation. Los Angeles officials estimate the balls will save about 300 million gallons of water each year.

The shade balls are BPA-free and should not release any chemicals. Garcetti said the orbs, which are manufactured by minority, women-owned facilities in Los Angeles County, require no parts, labor or maintenance aside from occasional rotation. They're recyclable and should last 10 years before they need to be replaced.

Plus, they're saving the city a lot of money compared to other alternatives, which included splitting the reservoir with a bisecting dam and installing floating covers that would have cost more than $300 million. According to a Facebook post from Garcetti, “with these shade balls, we ended up spending only $0.36 for each ball coming in at just $34.5 million to get the same result."

Shade balls aren't a new concept; they've been used in open-air reservoirs in Los Angeles since 2008. They're the brainchild of Dr. Brian White, a now-retired biologist with the Los Angeles Department of Water and Power, who said he got the idea when he learned about the application of “bird balls” that were placed in ponds along airfield runways to keep birds from congregating too close to planes.

In addition to the Los Angeles Reservoir, the balls are floating at Upper Stone, Elysian and Ivanhoe reservoirs and other areas.

There's something strangely mesmerizing about the rolling, bouncing balls. Watch as Las Virgenes Municipal Water District releases new shade balls in a reservoir:

Mary Jo DiLonardo Mary Jo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.