If he was not exhibiting the foot on the back while he was entangled with the fishing line, this is a good sign. In fact, this is actually normal behavior. Scientists believe that unlike a dog that can pant, a swan cannot pant to relieve heat from its body. It may indicate heat or stress by panting or gaping, but cannot dissipate the heat in this manner. There are many capillaries in the feet, very close to the top of the skin. Researchers believe that the capillaries help dissipate the heat. The swans place the feet on top of their backs to help get rid of the heat by holding it in the air. If the feet stay under water, the capillaries cannot conduct the dissipation of heat function.

Now, if the cygnet was entangled in the fishing line so that it could not move its foot and it was held in this manner at the time that the fishing line was engaged, then it could indicate an injury to the foot or leg. The Regal Swan