Feeding bread to wild ducks is incredibly harmful. Bread has almost no nutrients that are useful for the duck, so they become malnourished and more susceptible to disease. Compounding the problem is excessive bread in the water, which leads to high levels of E. coli and even botulism outbreaks. Wild ducks need to stay wild, and artificially feeding them causes them to lose their natural instincts for acquiring food. If you want to feed captive waterfowl, consider chopped vegetables, whole grains, or fruit instead.