Lake Champlain
In the colonial times, Lake Champlain gave an easily blocked water (or, in winter, ice) passage between the Saint Lawrence and the Hudson Valleys.  Boats and sledges were usually preferable to the unpaved and frequently mud-bound roads of the time.  The northern tip of the lake at Saint-Jean-sur-Richelieu, Quebec (St. John in colonial times) is a short distance from Montreal.  The southern tip at Whitehall (Skenesborough in colonial times) is a short distance from Saratoga, Glens Falls, and Albany, New York.