A swan's diet consists of plants, roots, leaves and seeds that it finds in its aquatic habitat. Some swans have adapted to eating grains and corn that they find on the ground. In some areas, swans will seek out farmland to eat the grains or corn, becoming a nuisance for farmers.
Swans eat while swimming and will dip their beaks into the water to scoop up algae and other surface plants. They may also dive under the water to pull up plants that grow from the bottom. It's not uncommon for swans to eat shellfish, but they do prefer a vegetable-based diet.