The Inner Tay Estuary is the inner, western part of the Firth of Tay, from the Tay Railway Bridge in the east to the Queen's Bridge over the River Tay in Perth and the bridge in Bridge of Earn on the River Earn.[citation needed] It is one of the largest estuaries in eastern Scotland, and is up to 2.5 km wide. It consists primarily of intertidal sand and mud flats extending seaward to the main channel, most of which are on the northern shore. Landward of these are salt marsh and Phragmites reedbeds. The estuary contains two large islands: Mugdrum Island, opposite Newburgh; and Moncreiffe Island, immediately below Perth. The estuary's narrow form, and the large volume of freshwater from the Rivers Tay and Earn, restrict the influence of saltwater west of the Tayport narrows. Much of the tidal water is freshwater or mildly brackish.