Carlingford Lough (; Ulster Scots: Carlinford Loch or Cairlinfurd Loch) is a glacial fjord or sea inlet that forms part of the border between Northern Ireland to the north and the Republic of Ireland to the south. On its northern shore is County Down and on its southern shore is County Louth. At its extreme interior angle (the northwest corner) it is fed by the Newry River and the Newry Canal.