Lake Nipissing, lake, southeastern Ontario, Canada. Lake Nipissing lies midway between the Ottawa River and Georgian Bay. It is 321 square miles (832 square km) in area and has a maximum length of 50 miles (80 km) and a maximum width of 30 miles (48 km). A remnant of glacial Lake Algonquin, which emptied eastward via the Ottawa River, Lake Nipissing (“little water”) is now drained by the French River westward to Georgian Bay. It was discovered by a French explorer, Étienne Brûlé, about 1610 and later served as a fur-trading route linking the Ottawa River with the upper Great Lakes.