Each year, bacterial contamination forces the closure of hundreds of acres of clam flats in southern Maine. These are the same bacteria that can pose a health risk at popular swimming beaches. Fecal coliform and E. coli bacteria are used as indicators that other, more harmful, pathogens may be present in coastal waters. But since wildlife, domestic animals, and humans can all be sources of fecal coliform, it is difficult for managers to identify the exact source of the bacteria.