The Carolinian forest zone covers most of the southwestern region of the province. The temperate and fertile Great Lakes-Saint Lawrence Valley in the south is part of the Eastern Great Lakes lowland forests ecoregion where the forest has now been largely replaced by agriculture, industrial and urban development. A well-known geographic feature is Niagara Falls, part of the Niagara Escarpment. The Saint Lawrence Seaway allows navigation to and from the Atlantic Ocean as far inland as Thunder Bay in Northwestern Ontario. Northern Ontario covers approximately 87% of the province's surface area; conversely Southern Ontario contains 94% of the population.