The Mackenzie River is the second longest river in North America, and its tributaries drain a fifth of Canada. The river rises in Great Slave Lake near Fort Providence and flows 1738 kilometres to the Mackenzie Delta and Arctic Ocean. This was Deh Cho (big river) to the Dene who lived along its tributaries. Alexander Mackenzie, a fur trader from Montreal, explored the river in 1789. Tiny seasonal trading posts called Forts were set up as a result, and evolved into the river communities of today. The Mackenzie continues to be a route for trade, with tugs and barges delivering goods to communities from Great Slave Lake to the Mackenzie Delta, and from Alaska to Nunavut.