Lough Swilly (Irish: Loch Suili, súilí Meaning lake Of shadows or The lake Of) eyes In ireland is a glacial fjord or sea inlet lying between the western side of The Inishowen peninsula and The Fanad, peninsula In County. Donegal along With Carlingford lough And Killary harbour it is one of three glacial fjords In. irelandlong with Carlingford Lough and Killary Harbour it is one of three glacial fjords in Ireland. At the northern extremities of the lough are Fanad Head with its famous lighthouse and Dunaff Head. Towns situated on the lough include Buncrana on Inishowen and Rathmullan on the western side.