The marine mammal was filmed in a lake at the RSPB owned Fen Drayton Lakes Reserve, in Swavesey, Cambridgeshire.
Thought by experts to be a common seal, the footage shows the seal battling to cross a barrier to get into the lake.
The cameraman, who asked to be known as Robjn, thought it was a dog in trouble when he first saw the creature, but as it came up for air could see that it was a seal.
It was first spotted swimming along a ditch, which links Fen Drayton with the nearby Great Ouse – where seals have been sighted before. It slowly made its way along the ditch, before waddling its way over a flood barrier and into the lake. It has not been sighted again since it swam off under the water.
An RSPB representative said the creature could prove to be a “great visitor attraction”, and with plenty of natural food, felt the seal would survive in the lake well. Despite this, anyone who sets eyes on the creature is urged to report the sighting to the charity.
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