Please, please don't!!!!! The very popular feeding of bread and other leftovers is not a complete food for the animals and can lead to digestive problems and other diseases. Moldy leftover bread is a particularly serious danger for all birds.
Excessive feeding affects the water quality and attracts unwanted guests, such as rats. These are then combated in large-scale poisoning campaigns, which results in the death of many other predators.
For those who really want to help:
Suitable feeds are mainly corn and other grains, cereal flakes, lettuce or commercially available duck feed.
Feed in shallow water or on the bank of the water so that the feed does not sink unused. Duck feed in pellet form is usually so light that it can be offered floating on the water surface.
Always only feed as much as the birds can eat immediately.
In many places, waterfowl are also provided with food by official bodies and are therefore not dependent on private feeding. In particular, feeding bans that have been imposed should be strictly observed.