Researchers expected that Talbert Marsh, a manmade saltwater wildlife habitat, would help keep the water near Huntington Beach in California clean; such wetlands are thought to purify contaminants as they flow out into the ocean. But in fact, the marshand its residentsmay be doing the exact opposite. A new study appearing in the June 15 issue of Environmental Science & Technology reveals that droppings from the marsh's seagulls are at least one major source of potentially hazardous bacteria that has been hitting the beachsometimes at levels thousands of times above the legal limit.

Stanley Grant of the University of California at Irvine and his colleagues tested the waters near Huntington Beach at more than a dozen sites, finding many instances of elevated enterococci bacteria levels. They also discovered that millions of gallons of bird droppings, flushed regularly from Talbert Marsh, can travel to the Pacific Ocean within less than 40 minutesleaving little time for saltwater and sunlight to kill the bacteria. "We have to be smarter about how we build these marshes," says Mark Sobsey of the University of North Carolina. "If they are designed so that the water goes through them very rapidly, the chances are pretty high that you'll have the same kinds of problems."

Grant notes that about 4.6 million saltwater marshes in the continental U.S. may be affected. "One scenario is that anywhere along the coast in the United States, you might run into this problem," he says. "We thought there were multiple sources for the bacteria at Huntington Beach. What we've found is that the marsh is one of those sources. This beach is ground zero of what could be a national problem."