Driving on Interstate 81 from Canada to Syracuse, New York

The rural surroundings finally end, albeit briefly, in the vicinity of Watertown, where I-81 intersects NY 3 in a commercialized area west of downtown Watertown. All four corners of the junction contain at least one shopping plaza, and the northwestern corner features the sprawling Salmon Run Mall. The commercial development follows I-81 north to its next exit, a diamond interchange with NY 12F near Jefferson Community College. At this point, I-81 turns northeastward, running south of an industrial park and north of the college before crossing the Black River to meet NY 12 in a less developed but still commercialized area north of the city. US 11 and I-81 finally part ways at this point, with I-81 continuing north toward Canada and US 11 heading northeast to serve some of the North Country's northernmost communities. As the highway leaves the Watertown area, it passes into another area of rolling, open terrain with only pockets of development in the immediate vicinity of the road's interchanges. NY 37 largely replaces US 11 as the paralleling surface route, and the state route follows I-81 for 13 miles (21 km) to the vicinity of Theresa. West of the village, I-81 intersects NY 411, a connector between La Fargeville and NY 37. While NY 37 continues north from Theresa, I-81 turns to the northwest, crossing increasingly isolated areas of the state to reach NY 12 on the south shore of the St. Lawrence River midway between Clayton and Alexandria Bay. From here, the freeway heads into the Thousand Islands on the first of several bridges known collectively as the Thousand Islands Bridge.[3] In the Thousand Islands, I-81 runs across Wellesley Island, one of the archipelago's largest. It initially heads northwest across the sparsely developed island, connecting to a pair of county-maintained roads before turning northeast at the eastern edge of Wellesley Island State Park. The freeway turns one final time near the northern edge of the island, curving back to the northwest at exit 52, the last exit along I-81. For most of its run on the island, I-81 runs along or close to the island's edge, permitting views of the river and some of the area's other islands. Not far from exit 52, an interchange linking the freeway to a paralleling local road, I-81 crosses the International Rift on a 90-foot (27 m) bridge connecting Wellesley Island in New York to Hill Island in Ontario, Canada. From here, the road continues north to Highway 401 as Highway 137. The long, continuous bridge span between Wellesley Island and the United States mainland is one of the few remaining two-lane stretches left on the Interstate Highway System