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 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.