The foot was probably amputated by a predator such as a snapping or soft-shelled turtle. She may limp, but as long as she is able to get up and down banks, then she can survive. Can she fly? Is she a wild swan?

If she is a captive swan and cannot fly, then you might be able to capture her and have an avian veterinarian check out the injury. However, you must wait until the cygnets get old enough so that the male can look after them by himself for a couple of hours. If she is able to care for the cygnets and herself and there does not appear to be anything oozing or seeping, it is probably an old injury and no immediate attention is required. If she starts having more difficulty in getting around, then, you will need to seek immediate veterinary medical attention. The Regal Swan