The Golden Triangle is an informal designation for a region renowned as one of the premier fly fishing locations in the United States. The region is named for its approximate boundaries that form an equilateral triangle having an apex at Glacier National Park and encompassing Yellowstone National Park and the eastern portion of Idaho. Superior fly fishing also exists in the surrounding areas of the Rocky Mountains in Idaho and western Montana.
Because of a large number of major rivers such as the Yellowstone, Madison, Gallatin, and the Blackfoot, many hundreds of fast, clear-running streams and high alpine lakes, the region contains a large number of trout. Species such as brook, rainbow, brown, cutthroat, Dolly Varden, and golden trout are plentiful in this area, generally wild, and range in size from a few ounces to several pounds.