 -- The Los Angeles Reservoir looks like a giant ball pit.

The city poured 96 million, black, four-inch plastic balls over the surface of its 175-acre reservoir earlier this week - the first city in the country to use shade balls to preserve its water sources, officials said.

On his cue of “balls away,” Mayor Eric Garcetti released the final 20,000 shade balls into the reservoir on Monday in the city’s effort to conserve water and maintain the reservoir’s water quality.

“By reducing evaporation, these shade balls will conserve 300 million gallons of water each year,” Garcetti told ABC station KABC. “Instead of just evaporating into the sky, that’s 300 million gallons to fight this drought.”

The shade balls can last about 10 years before the LA Department of Water and Power will remove, recycle and replace them, KABC reported.

“This is a blend of how engineering really meets common sense. We saved a lot of money, we did all the right things,” LADWP general manager Marcie Edwards told KABC.

The city was able to purchase each plastic shade ball for 36 cents each, costing the city far less than its initial $300 million estimate to cover the reservoir, according to officials.

One expensive alternative to the shade balls included splitting the reservoir into two by building a bisecting dam and using two floating covers to protect the water, officials said.

The LA Reservoir holds 3.3 billion gallons of water, which could supply water to the entire city for up to three weeks, officials said.

Mayor Garcetti’s office did not immediately respond to ABC News’ request for additional comment.