Police have started an investigation after a marina manager suffered a leg injury when he was allegedly pushed into the water.
The coastguard was called to Poole Quay Boat Haven on Monday to rescue the man who had fallen from a speed boat.
A spokesman said it appeared the boat had been impounded at the harbour in lieu of payment and two men had turned up with bolt cutters to free it.
Dorset police were called after reports that a theft was in progress.
A spokesman said no arrests were made.