Thousand Islands level year-round, and support at least two living trees. The Thousand Islands archipelago is located at the outlet of Lake Ontario at the head of the Saint Lawrence River. The region is bisected by the Canada–United States border and covers portions of Jefferson and St. Lawrence counties in the U.S. state of New York, in addition to parts of the United Counties of Leeds and Grenville and Frontenac County in the Canadian province of Ontario. Geologically, most of the islands are located where a branch of the Canadian Shield runs south across the river to join with the Adirondacks. The
North American river otter leaves, grass, moss, bark, and hair. Den sites include burrows dug by woodchucks ("Marmota monax"), red foxes ("Vulpes vulpes"), nutria ("Myocastor coypus"), or beaver and muskrat lodges. North American river otters also may use hollow trees or logs, undercut banks, rock formations, backwater sloughs, and flood debris. The use of den and resting sites is chiefly opportunistic, although locations that provide protection and seclusion are preferred. Aquatic life ties North American river otters almost exclusively to permanent watersheds. The North American river otters favor bog lakes with banked shores containing semiaquatic mammal burrows and lakes with beaver lodges. The North