The man was first spotted by a member of a cargo ship's crew (pictured right)
A man has survived treading water for four hours in a busy shipping lane in the Thames Estuary before being saved by a lifeboat.
He was plucked from a two mile-wide (3km) stretch of water by Gravesend RNLI's crew after being spotted by someone on a passing cargo ship.
The man drifted for four miles (6km) after going into the water at Southend.
"I have never heard of anyone treading water for four hours before," said Gravesend RNLI spokesman Alan Carr.
"He was extremely lucky."
The victim, who was wearing just a pair of trousers, was pulled to safety by the inshore lifeboat's three crewmen at about 09:20 BST on Wednesday.
'Eagle-eyed' crewman
"He was extremely cold and had swallowed a lot of water and was quite happy to be on the firmer ground of the lifeboat," said Mr Carr.
"He had no lifejacket on - any longer and the outcome could have been quite different.
"If he had not been spotted by an eagle-eyed person on the ship, I am not quite sure what would have happened to him."
The cargo ship's engines were switched off and the crew kept a watch over the man while the lifeboat was radioed.
The man was rescued from the edge of the shipping lane between Canvey Island in Essex and Allhallows in Kent.
He was wrapped in a blanket and then transferred to an ambulance at Holehaven Creek slipway in Essex.
Mr Carr said it was not known why the man was in the water.
