The male common seal, who has been in his new surroundings for around a week, could be rescued and returned to the sea next week.
The out-of-sorts seal has been spotted at Topcliffe Weir in Thirsk. It is believed to have followed fish around 50 miles from the North Sea up the River Swale.
And if he hasn't made his way back home by next week the British Divers Marine Life Rescue could be forced to intervene.
Julia Cable of the British Divers Marine Life Rescue, who are hoping to organising the rescue attempt, said: “There is a male common seal which has been in the area for about a week.
“We are currently trying to gain an idea of its movements, where it is going and when.
“It is not in danger but it is in everyone’s best interests for it not to be there.
“It is being monitored by locals at the moment.”
The seal wouldn’t be able to be tranquilised for fear of drowning, so a large weighted net would have to be used to capture the rogue mammal.
“We are trying to work out the best place and time to get a weighted net in the river,” Julia added.
“We will then stretch it out across the river but unfortunately it’s still not still enough on the water to be able to do it just yet.
“We’d have to know where the seal is as they are so quick and strong in the water and this is quite a large one, so it will be difficult."
IT isn't the first time a seal has swam in-land looking for food, although it could be the furthest from the coast that one has been spotted.
Bex Lynam, The Yorkshire Wildlife Trust’s North Sea Marine Advocacy Officer, said: “Seals are known to use a number of the UK’s rivers and on occasions will swim upriver for quite some distance.
“It’s thought that they are simply following their food source which would include salmon or sea trout making their way up the river at particular times of the year.
“They may then become disorientated, especially younger seals, which is why they have been reported found in fields and similar unusual locations, having hauled themselves out of the river and on to dry land.”