Swans must have water for eating (swans can choke if they do not have water while eating), drinking (or swans can become dehydrated ), bathing and preening (to keep their feathers healthy), and mating. Water is essential in warm weather to keep the swans cool and prevent stress and high body temperature which can possibly kill the swan. Water also provides the swans and their young (cygnets) shelter from land predators.

Finally, without water, there would be no aquatic vegetation from which the swans eat, seek shelter and nest. The Regal Swan