According to Susan Freinkel, writing in LiveScience, “America's 83 million pet dogs produce some 10.6 million tons of poop every year. That's enough to fill a line of tractor-trailers from Seattle to Boston."
Studies have traced 20 to 30 percent of the bacteria in water samples from urban watersheds to dog waste. Just two to three days of waste from 100 dogs can contribute enough bacteria, nitrogen and phosphorous to close 20 miles of a bay-watershed to swimming and shellfishing, according to the U.S. Environmental Protection Agency. It also can get into the air we breathe: a recent study of air samples in Cleveland, Ohio, and Detroit, Mich. found that 10 to 50 percent of the bacteria came from dog poop.