At 230 miles, the Shannon is Ireland's longest river. It flows from Lough Allen, and Loughs Ree and Derg are also on its course. At Limerick, the river widens into its namesake estuary and runs for 50 more miles before it enters the Atlantic. Peat bogs and marshes line the river for much of its course, and the Shannon is considered a dividing line between Ireland's more cultivated east and wild west. A chief tributary is the Suck River. The Shannon does not pass through Dublin, although the Liffey does.