That bread you're tossing to the ducks malnourishes the adults and can leave the babies unable to fly for the rest of their lives.
Bread is junk food for a duck. It fills them up so they quit foraging for the bugs, plants, and seeds that actually feed them.
In a growing duckling, a diet that heavy in empty carbs makes the wing grow too fast and twist at the joint. The feathers jut out sideways, the wing never works right, and the bird is grounded for good. It's called angel wing, and in an adult it can't be undone.
It doesn't stop at the birds. A pond where people dump bread gets crowded and aggressive, ducklings never learn to find their own food, and the soggy leftovers rot into algae blooms and draw rats.
If you want to feed them, give them food, not filler: cracked corn, oats, halved grapes, chopped lettuce, a handful of thawed peas.
Better yet, just watch them. A healthy pond already feeds its ducks. They were doing fine before the bread showed up.