Michael Poole and his family thought it would just be a ‘normal dog walk’ when they headed for the bank of the river on Boxing Day.
However, it proved to be anything but as they ended up helping to rescue the seal - which they’ve called Sid - after calling in the RSPCA.
Michael told the News: “This is one walk - and one Christmas - we will always remember!”
Michael was with his wife, two children and two dogs when they spotted two lads ‘larking about’ on the river bank behind Tattershall Castle.
He adds: “It was only when we got closer that we noticed the seal in the water.
“It was distressed because of the weir which meant it couldn’t get any further.
“It didn’t know what to do but it somehow managed to climb on to the bank although you could tell it was struggling.
“It was bizarre.
“A young seal was the last thing we expected to see in the River Bain!”
The seal managed to clambered to the top of the embankment and down into an adjoining field.
Michael and his family phoned the RSPCA who promised to send an inspector.
Michael added: “When I told them where we were, there was silence on the other end of the phone.
“I don’t think they really believe it.
“The seal must have swum up the Witham from the Boston and The Wash and then into the Bain.
“It must be 15 miles - and all against a flood tide.
“We were astonished.”
Michael says the RSPCA advised the family not to approach the seal and to make sure their two dogs stayed well clear.
He added: “They might look cute but apparently, young seals can give you a nasty bite.”
Michael says it took around 40 minutes for the inspector to arrive from the Grantham area.
He explained: “She was brilliant. She was trained for this sort of thing but she was amazed as the rest of us.
“She said seals can often be found a couple of miles inland - but not this far.
“She had never heard of anything like it before.”
The inspector managed to get the seal into a special protective ‘bag’ and took it away from the scene.
Michael said: “She told us it only weighed 14kgs when it should have been around 30kgs.
“She also told us seals often die in fresh water. This one must have been very lucky.”
Sid was taken to a rescue centre where he is receiving specialist treatment but Michael says it is hoped to release him back into the North Sea in Norfolk.
He added: “We’re keeping in touch and it would be great to watch that happen.”