in area of all landlocked states. The Green Mountains in Vermont form a north–south spine running most of the length of the state, slightly west of its center. In the southwest portion of the state are located the Taconic Mountains. In the northwest, near Lake Champlain, is the fertile Champlain Valley. In the south of the valley is Lake Bomoseen. The west bank of the Connecticut River marks the state's eastern border with New Hampshire, though much of the river flows within New Hampshire's territory. 41% of Vermont's land area is part of the Connecticut River's watershed. Lake Champlain, the sixth-largest body of fresh water in the United States, separates Vermont from New York in the northwest portion of the state. From north to south, Vermont is long. Its greatest width, from east to west, is at the Canada–U.S. border; the narrowest width is near the Massachusetts border. The width averages . The state's geographic center is approximately east of Roxbury, in Washington County. There are fifteen U.S. federal border crossings between Vermont and Canada. Several mountains have timberlines with delicate year-round alpine ecosystems, including Mount Mansfield, the highest mountain in the state; Killington Peak, the second-highest; Camel's Hump, the state's third-highest; and Mount Abraham, the fifth-highest peak. Areas in Vermont administered by the National Park Service include the Marsh-Billings-Rockefeller National Historical Park (in Woodstock) and the Appalachian National Scenic Trail. The topography and climate make sections of Vermont subject to large-scale flooding. Incidents include the Great Vermont Flood of 1927, which killed 84 and damaged much of the state's infrastructure, the flood of 1973, which covered many of the state's roads in the southeast, and Tropical Storm Irene in 2011, which caused substantial damage throughout the state. In response to the 1927 flood, the Federal government funded construction of six flood control dams in the state, run by the Army Corps of Engineers. These extreme rain and flooding events are expected to get worse with climate change. Cities Vermont has ten incorporated cities. The most populous city in Vermont is Burlington. Its metropolitan area is also the most populous in the state, with an estimate of 225,562 as of 2020. Largest towns Although these towns are large enough to be considered cities, they are not incorporated as such. Climate The annual mean temperature for the state is . Vermont has a humid continental climate, with muddy springs, in general