I suppose it is fair to say that The Boyne is our most famous river: a battle of great importance was fought there; Fionn McCool lived on its banks; so does Sean Boylan.
Some people think of Sean as a witch doctor: that is unfair, he is a herbalist, even if occasionally he is seen flying on a broomstick on All Souls' Night. Fionn was a wise man too but his wisdom came by accident rather than from herbs. One day while cooking a salmon that he had caught in that famous river, he burned the thumb of his right hand; he put it to his lips to cool it -- a miracle occurred.
Suddenly some things that had been puzzling him became clear -- that gift never left him. It served him well on one occasion when otherwise he might have done his right-hand man a grave injustice. His warriors, The Fianna, had been down the country hunting; on their way back they had to cross The Blackwater near Mallow. It was wide and deep. A little old lady was in distress on the bank wondering how she would get across. All but one of the warriors ignored her and used their spears to vault the river. Oisin put her on his back and swam across.