is the only major river in the Northeastern United States without a port at its mouth. Mouth and tidelands The Connecticut River carries a heavy amount of silt from as far north as Quebec, especially during the spring snow melt. This results in a large sandbar near the river's mouth which is a formidable obstacle to navigation. The Connecticut is one of the few major rivers in the United States without a major city at its mouth because of this obstacle. Major cities on the Connecticut River are Hartford and Springfield, which lie upriver respectively. The Nature Conservancy named the Connecticut River's tidelands one of the Western Hemisphere's "40 Last Great Places", while the Ramsar Convention on Wetlands listed its estuary and tidal wetlands as one of 1,759 wetlands of international importance. In 1997, the Connecticut River was designated one of only 14 American Heritage Rivers, which recognized its "distinctive natural, economic, agricultural, scenic, historic, cultural, and recreational qualities." In May 2012, the Connecticut River was designated America's first National Blueway in recognition of the restoration and preservation efforts on the river. Dams The Connecticut River's flow is slowed by main stem dams, which create a series of slow-flowing basins from Lake Francis Dam in Pittsburg, New Hampshire, to the Holyoke Dam at South Hadley Falls in Massachusetts. Among the most extensively dammed rivers in the United States, the Connecticut may soon flow at a more natural pace, according to scientists at the University of Massachusetts at Amherst, who have devised a computer that – "in an effort to balance human and natural needs" – coordinates the holding and releasing of water between the river's 54 largest dams. The Cabot and Turners Falls hydroelectric stations generate up to 68 MW. The Holyoke Canal System and Hadley Falls Station at Holyoke Dam are rated a combined 48 MW. Tributaries The Connecticut River watershed encompasses , connecting 148 tributaries, including 38 major rivers and numerous lakes and ponds. Major tributaries include (from north to south) the Passumpsic, Ammonoosuc, White, Black, West, Ashuelot, Millers, Deerfield, Chicopee, Westfield, and Farmington rivers. The Swift River, a tributary of the Chicopee, has been dammed and largely replaced by the Quabbin Reservoir which provides water to the Massachusetts Water Resources Authority district in eastern Massachusetts, including Boston and its metropolitan area. Ecology Along its southern reaches, the Connecticut River has carved a wide, fertile floodplain valley (known