Shannon, the largest river of Ireland, rises in the Cuilcagh Mountains, County Cavan, and falls after a course of 254 miles into the Atlantic Ocean between Loop Head and Kerry Head. It flows SW. to Lough Allen in Leitrim; thence S. through a succession of expansions - Loughs Boderg, Bofin, Forbes, Ree, and Derg - past the towns of Carrick, Athlone, and Killaloe, to Limerick; and finally W., forming a wide estuary some 70 miles long and 10 miles across at its seaward extremity. About 10 miles from the entrance the river narrows to 1 1/2 mile in width. Outward navigation commences at Foynes, connected by railway with Limerick. Vessels of 1000 tons can get up to Limerick, and small steamers to Athlone; boats ascend to beyond Lough Allen. The Suck and Fergus enter from the right, and the Inny, Brosna, Mulkear, Maigue, and Deel from the left. The river is canalised for some distance below Athlone, and between Killaloe and Limerick; and it is connected with Dublin by the Grand and Royal Canals.