1. Ivanhoe Reservoir, Los AngelesPhoto: Gerd Ludwig in 2007, high levels of bromate - a carcinogen formed when bromide and chlorine react with sunlight - were found in Los Angeles’s Ivanhoe Reservoir. Today three million black plastic balls help deflect UV rays.

    Ivanhoe Reservoir, Los Angeles
    Photo: Gerd Ludwig

    in 2007, high levels of bromate - a carcinogen formed when bromide and chlorine react with sunlight - were found in Los Angeles’s Ivanhoe Reservoir. Today three million black plastic balls help deflect UV rays.