Watery and smelly belly button may be caused by: 1) umbiliculitis, umbilical abscess formation; 2) umbilical intestinal fistula; 3) umbilical urinary leakage. If the navel is running and there is purulent discharge, it is considered to be caused by umbiliculitis and umbilical abscess formation. If the fluid flowing out is feces mixed with food residue, it is considered to be caused by umbilical fistula. If the discharge smells like urine, it is considered to be caused by umbilical-urinary fistula. If there is water flowing from the umbilicus and it smells bad, it is recommended to visit the hospital for a physical examination and, if necessary, a CT or magnetic resonance examination to clarify the diagnosis.