Any bird that seems to be unkempt when it usually has clean straightened feathers is either suffering from stress or some type of possible infection such as a bacterial, fungal, parasitic, etc. If you can capture the swan (dependent upon able to fly or wild), then you might want to have it looked at by a veterinarian to determine what might be wrong with its feathers. If the swan does not stay clean or is unable to take care of its feathers, it can succumb to drowning because the feathers won't be water repellent or die from an illness such as pneumonia or other condition because it can't stay warm or dry. The Regal Swan