Duck with undercarriage!

[evie72]

Hi I am new to this site and just finding my way around. We have a problem with one of our Khaki Campbells who has developed a large undercarriage.
When checked it feels like a large squidgy water ballon and though it does not seem to cause her pain must be uncomfortable and she cannot get out of the small pond! There does not appear to be any sign of a prolapse. Does anyone have an idea as to what may be causing this and any cure? Thank you