Josh,
I am SURE some folks stayed behind, that was before the Famine. The Family name was Fee.
Had a great dinner in Mallow about 16 years ago at a little place called The Black Lamb [http://homepage.eircom.net/~blacklambinc/]. My sisters and I had brought my Mother to Ireland on a visit. You would have thought we were all wearing halos the way we were treated. The place we stayed was the Longueville House [http://www.longuevillehouse.ie/] Pretty nice.
It was not a fishing trip for me, but try a Google search on Blackwater River ireland - bet you find something - or ask in the local pub in Mallow.
Have a great time