These images appeared recently relating to a project in Los Angeles, related to the restoration of water reservoir levels of bromate. A past post outlined similar situations in Silver and Elysian Lakes and the use of phytoremediation to eliminate levels. A new approach is the use of sun-block, in the form of plastic balls, that limit the mixing of bromide and chlorine which is causing elevated levels of bromate.
A summary from a post in Boston.com: "Department of Water and Power workers are emptying out bales of plastic balls in the Ivanhoe reservoir in Los Angeles on Monday, June 9, 2008. Department of Water and Power released about 400,000 black plastic 4-inch balls as the first installment of approximately 3 million to form a floating cover over 7 acres of the reservoir to protect the water from sunlight. When sunlight mixes with the bromide and chlorine in Ivanhoe's water, the carcinogen bromate can form."
:: images via Boston.com
From the LA Times: "Open reservoirs exposed to sunlight are now rare. The area's reservoirs -- Silver Lake, Ivanhoe and Elysian -- first registered elevated levels of bromate between June and October 2007. But state health officials said the dangers were minimal because bromate poses a small cancer risk only after consumed daily over a lifetime.But the discovery of bromate prompted officials to look for ways of shading Elysian and Ivanhoe. A tarp would have been too expensive and a metal cover would take too long to install, especially in a year of drought. So one of the DWP's biologists, Brian White, suggested "bird balls," commonly used by airports to prevent birds from congregating in wet areas alongside runways.Ivanhoe and Elysian reservoirs will be blanketed by about 3 million balls each for about four years."
:: image via LA Times
It would be interesting to see if this could be a pre-emptive method of reducing bromate production, or other potential toxic issues. Aside from the more common use of airport protection, this extreme (yet simple) method could have some additional uses in sunlight-driven water pollution, including algal blooms which deplete the waterways of oxygen, resulting in eutrophication. Also, it could be used to cool water temperatures to improve fish habitat. Some other options I found would be heat retention, odor control, evaporation control, and vapor containment.
:: use of bird balls - image via Euromatic