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."
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A police officer has been taken to hospital with serious leg injuries after being hit by a car in a Bedfordshire town.
Cloudy with rain at first, this becoming heavier for a time.
A man who was found dead in a multi-storey car park in Colchester has been provisionally named by police.