Hi Victoria
You need to remove her from the water if she is in the water. If she is unable to hold her neck up she may have ingested a toxin. If the neck is held up, but looks stiff, she may have sustained an injury or possibly has something lodged in her throat. In any case, we would strongly urge you to capture her and take her to a licensed waterfowl/avian veterinarian as soon as possible. If she stops eating or drinking she can become severely dehydrated and develop other health issues. The veterinarian may have to tube feed her and/or give her an i.v. for rehydration/digestion purposes. Please let us know how she is doing. The Regal Swan