Farmer Robert Patchett said the year-old heifers, which may charge if approached by strangers, must have swum from Faxfleet Grange farm in Goole, North Humberside, after trying to escape a big cat locals believe is on the loose. Mr Patchett, who farms 1,000 acres, said: "If I had not seen it with my own eyes I would not have believed it. They just swam out into the river and it was sheer good fortune there was an island. The estuary is one mile wide here and very dangerous. There is a danger the river could flood and wash the cows off, so we want to get them off as soon as possible."