North Wales Police are appealing for witnesses after emergency services pulled a man from the River Dee at Llangollen, Denbighshire.
Police said they were called to a bridge over the river at about 2000 BST on Tuesday, where the man was described as in a "distressed situation".
Trained negotiators talked to him for nearly 90 minutes before he fell about 20ft (six metres) into the water.
The man is in hospital in a stable condition with serious injuries.
North Wales Police had cordoned off the area after being called at 1951 BST.
Castle Street had been closed, and it re-opened about an hour later.
Anyone with information is asked to contact the police and fire service joint control room on 101, quoting incident reference number L157814.