We know for a fact, through x-rays and necropsies, that swans can get arthritis due to injury and/or old age. If the swan could not use his legs and walk, enter or exit water, it was going to suffer immensely.

When caught early, we have successfully used medication to mitigate pain and swelling. However, this was in a captive setting where the swan could be administered the medication on a daily basis. The swan in a wild setting would have to be captured and placed in a captive setting with no guarantees that medication would or would not work in this case due to the unknown extent of the condition. The Regal Swan