Lough, a lake of Ireland, province of Ulster, bounded N. and E. by Antrim county, W. by Tyrone, and S. by Armagh. It is the most extensive lake in the United Kingdom, and one of the largest in Europe, measuring 18 miles in length by 11 in breadth, and covering an area of 98,255 acres. The height of its surface above the level of the sea at low water is 48 feet, and its greatest depth is 102 feet. The lake is far from picturesque, and contrasts unfavourably with the other loughs of Ireland. Its shores are low and flat, and frequently become flooded after heavy rains. There are several islets, one of which, Ram's Island, is 6 acres in extent, and contains the remains of a round tower. The principal streams which flow into the lake are the Blackwater, the Upper Bann, and the Six-Mile Water; and its only outlet is the Lower Bann, which leaves the lough at its N.W. corner, and after flowing through Lough Beg, enters the sea near Coleraine. It is connected by canals with Belfast, Newry, and Lough Erne. It is navigated by small vessels; and one or two commodious ports or harbours are stationed along its coasts. The waters of the lough have strong petrifying qualities, and the petrification is sili- cious and susceptible of a beautiful polish. The fish most abundant are the pollen (Coregonus pollen), a bright silvery fish, resembling the herring; and the dolgahern, a species of trout. Numbers of aquatic birds, such as the heron, widgeon, &c., frequent the shores.