Watched the first episode of Nick Crane’s Britannia, about England and Wales, and was interested to see a section about Snowdonia which implied that William Camden, the Elizabethan author of the original Britannia, had said that there were was a lake there which had a floating island in it. It implied that Camden would have come across this story by talking to cattle farmers of the area on his travels through North Wales. But that doesn’t seem to be the case at all, in fact the English translation of Camden’s own text says:
Neverthelesse, so ranke are they with grasse that it is a very comon speech among the Welsh, that the mountaines Eriry will yeeld sufficient pasture for all the cattaile in Wales, if they were put upon them together. Concerning the two Meare [lakes] on the toppe of these, in the one of which floteth a wandering Island, and in the other is found great store of fishes, but having all of them but one eye apeece, I will say nothing lest I might seeme to foster fables, although some, confident upon the authority of Giraldus, have beleeved it for a verity.
the latter of which are said to be of so great an extent, that if all the herds in Wales were collected together, they would supply them with pasture for a considerable time. Upon them are two lakes, one of which has a floating island; and the other contains fish having only one eye, as we have related in our Itinerary.
Even then Giraldus is just summarising what he wrote in his “The Itinerary of Archbishop Baldwin through Wales” (1188 CE), where he says:
On the highest parts of these mountains are two lakes worthy of admiration. The one has a floating island in it, which is often driven from one side to the other by the force of the winds; and the shepherds behold with astonishment their cattle, whilst feeding, carried to the distant parts of the lake. A part of the bank naturally bound together by the roots of willows and other shrubs may have been broken off, and increased by the alluvion of the earth from the shore; and being continually agitated by the winds, which in so elevated a situation blow with great violence, it cannot reunite itself firmly with the banks. The other lake is noted for a wonderful and singular miracle. It contains three sorts of fish – eels, trout, and perch, all of which have only one eye, the left being wanting; but if the curious reader should demand of me the explanation of so extraordinary a circumstance, I cannot presume to satisfy him.
So sadly it appears that William Camden was just referring back to a text that was almost 400 years old when the first edition of Britannia was published in 1586.