Hants Avon, Longford Estate, Charlton Dairy Shallows, April-May 1971, I was showing a new salmon rod to the Estate the well-known lies (asked to do so by keeper, Tom Williams, who had shown me them as a kid a few years earlier), inviting the man to have a chuck now and again- to have a test fish in a particular spot - then suggesting he add more lead, hold the rod out more or higher, fish the spinning lure or plug slower etc...
Then we came across four or five big barbel laying into spawning minnow shoals on the shallows. Out went a # 3 Mepp from the new rod - WHACK! - instant take, barbel on. The fish tore off downriver into deeper water, and the angler, not up to much as a fisher, pulled too hard on it and straightened the spinner's treble hook. BIG barbel (double)
So, it happens.