Seeking creative solutions to a water quality control problem, the Los Angeles Department of Water and Power began pouring some three million polyethylene balls into the Ivanhoe Reservoir in the summer of 2008.

The reservoir water had concentrations of naturally occurring bromide and bacteria-killing chlorine additives, and when that combination is exposed to UV rays bromate is produced—an unwanted carcinogen in 58 million gallons (220 million liters) of water used by some 600,000 Angelenos.

Engineers flooded the surface with the same type of balls that airports use to keep birds from flocking to wetlands beside runways, where they create a hazard to aviation. This solution isn't typical, because open-air reservoirs containing chlorine are increasingly rare. But water quality problems abound and their control is an increasingly important green job around the world.

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