The historic assemblage of fish species in Glacier National Park is restricted in number due to the relatively recent withdrawal of continental glaciers from the region. The human urge to tinker with natural systems is no better illustrated than in the park fishery, which has been radically changed by human manipulations. Lake trout (also called mackinaw), historically found only in park waters draining to Hudson Bay, now occur in most of of the large lakes west of the Continental Divide. However, there is no evidence that non-native lake trout were directly stocked in park waters. They apparently became established in several of the park's west side lakes through migration from the lower Flathead River system where they were introduced during the early 1900s.