Original: Geographical features include Great Bear Lake , the largest lake entirely within Canada , Great Bear Lake Keller Lake and Great Slave Lakes , as well as the Mackenzie River and the canyons of the Nahanni National Park Reserve , a national park and UNESCO World Heritage Site .
Simplified: The Northwest Territories have many geographical features , like the Great Bear Lake , the Mackenzie River and Nahanni River , which is a national park and a UNESCO World Heritage Site .