Strangford Lough, inlet of the Irish Sea between the Ards and North Down district and the Newry, Mourne and Down district, Northern Ireland.
The lough (lake) is about 16 miles (26 km) long and 4 miles (6 km) wide and has a very narrow entrance, which cuts across the northeast-southwest trend of the rocks in the area. The edges of the lough are characterized by many drumlins, or long oval mounds, which are also seen in submerged form in the lough. Strangford Lough afforded sheltered entry to northeastern Ireland from early times, and there is plentiful evidence of old settlements around its shores.