Hunstanton lifeboat was launched after a man was reported to have jumped off the Freebridge into the River Ouse.
RNLI volunteer crew Gavin Grange, Ian Devenny, Michael Wallace and Victor Dade launched after the alarm was raised at 7.55pm on Saturday.
Five minutes after they set off for Lynn, the coastguard said the man was out of the water but struggling in the mud.
They requested the boat to proceed to the scene until it was confirmed that the person was safe, but the lifeboat was stood down two minutes later after it was reported that the man was in police custody.
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