The animal has been given a temporary home in the town while efforts are made to return it to Leverburgh where it is looked after by local fishermen.
Argyll Animal Aid said it was one of a group of feral cats that fishermen use to control rat and mice populations.
The charity hopes transport can be found for its return journey.
Jean Sutherland, of Argyll Animal Aid, told BBC Radio Scotland, the female cat had boarded a chartered yacht.
She added: "It was found on Friday by a lady and being an animal lover she managed to coax it into a carrier and took it to a local vet.
"They have looked after it over the weekend to check all is well and in between times we have been trying to find out where it had come from."
A cat that sneaked onboard a yacht on the Isle of Harris in the Western Isles ended up about 200 nautical miles away in Oban in Argyll.