Geographically, the region is largely south of the tree line, which runs roughly northwest to southeast, from the Mackenzie River delta in the Arctic Ocean to the southeastern corner of the territory. Tundra characterizes the land north of the tree line; there the native inhabitants depend on hunting, fur-trapping, and making arts and crafts for income, and obtain many necessities from fish, seals, reindeer, and caribou. Most of the development in the territory has taken place south of the tree line, where the land is well covered with soft woods and rich in minerals. Here, too, are two of the largest lakes in the world, Great Slave and Great Bear, linked to the Arctic Ocean by one of the world's longest rivers, the Mackenzie, which runs 1,120 mi (1,800 km) from its source in Great Slave Lake. The Northwest Territories are the site of the northern end of Wood Buffalo National Park (est. 1922) and all of Nahanni National Park (est. 1972).