A spokesman for Norfolk Police said:
"The man was retrieved from the water and was taken to Addenbrooke's Hospital by air ambulance for treatment. He is currently described as being in a critical condition.
"Police and the Health and Safety Executive are carrying out a joint investigation into the incident."
More top news
Mild overnight with a few light showers. Breezy tomorrow. Generally dry and settled with some decent sunny spells
Norwich City have signed West Brom midfielder Graham Dorrans on a permanent deal.
A mother whose baby was found dead in a village pond in Norfolk will not face criminal charges because she has already suffered enough.