“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. The seal apparently got lost while chasing fishCredit: Karen Hargreave “My husband and I decided to try our luck on Friday morning, and sure enough he was still there, out on the bank. He was an amazing sight.”He was also spotted by walker Tony Wilson, 48, who thought the animal was a sheep.Mr Wilson said: “It looked so bizarre. At first I thought it was a sheep but as I got closer I saw he was a great big grey seal. I couldn’t figure out how he’d arrived there but speaking to people in the village later it seems he’d swam all the way from the sea up the river.”Sea life experts were impressed by the “incredible” journey the seal made. Head Curator at Sea Life Manchester, Alan Kwan told The Telegraph: “It’s true what they say, there’s no such thing as a free dinner, even in the animal world! It’s likely the seal hankered after a particularly dishy fish – so much so that the seal gave chase for 50 miles! Seals are incredible animals, the transition from sea to freshwater wouldn’t have bothered him at all.” “When I saw the message, I rang my friend as I couldn’t quite believe it. She confirmed the sighting .but also said that it had since disappeared. She said: “Some friends of ours went for a walk, and saw something large in the river. “On closer inspection they realised it was a seal and as I am interested in wildlife they messaged me. “Apparently the seal had turned up last Thursday morning. Locals from the mill spoke to various experts, some I think may have visited the site, and confirmed it was a large healthy male. “He had probably swum up from the Humber estuary following salmon. When ramblers spotted a large grey creature basking in the Yorkshire Dales, they assumed it was a sheep. However, it turned out to be a determined seal, which swam 50 miles through Britain’s river network from the North Sea in pursuit of fish.The long-distance swimmer had most likely become lost and disorientated after chasing a salmon or sea trout upstream, according to experts.The seal is thought to have swum through York on its way to the Dales, in pursuit of fresh Spring salmon.Seals are mammals which usually prefer a salt water marine environment, as this is where most of the fish they can eat are found, but can also swim in fresh water, and do this when they chase their food sources up rivers.Anthony Hurd, the Yorkshire Wildlife Trust’s Living Seas Centre Manager in Flamborough, said it is not rare for seals to travel upstream in search of food, but that it is “surprising” the animal was spotted so far inland. It is thought by the Trust that the animal became lost while on its journey to catch fish.Bex Lynam, The Trust’s North Sea Marine Advocacy Officer, told The Telegraph: “Seals are known to use a number of the UK’s rivers and on occasions will swim upriver for quite some distance. “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.”Seals are mammals which usually prefer a salt water marine environment, as this is where most of the fish they can eat are found, but can also swim in fresh water, and do this when they chase their food sources up rivers.Walkers were stunned to see the large grey male seal near Thirsk, at a spot near Topcliffe Weir.He was pictured by amateur photographer Karen Hargreave, from the area, who said she had never seen anything like it before. The seal was seen swimming in the weirCredit:Topcliffe Weir Facebook Page Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.