3. The mouth of the Clanrye River flowing into Carlingford Lough is hereby defined to be a straight line, marked M on the map or plan in the Schedule and drawn in a line bearing 236° 60’ true from the point marked O on the said map or plan at Irish Grid Reference point J14470, 17885 in the County of Down in Northern Ireland, to the point marked P on the said map or plan at Irish Grid Reference point J13920, 17049 in the County of Louth in the Republic of Ireland; and the point or points of the mouth of the Clanrye River from which distances are to be measured under the Foyle Fisheries Acts are hereby defined to be any and every point on the aforesaid straight line marked M.