The Bighorn River begins at Boysen Reservoir in Wyoming and flows over 400 miles. It is joined by the Little Bighorn River near the town of Hardin before traveling roughly 50 more miles and dumping into the Yellowstone River. The river is a high quality and popular fly fishing location through the entire year, including winter. The river consistently delivers large rainbow and brown trout. The upper section of the river receives the highest pressure, typically in the middle summer months. Further down river the Bighorn begins to slow as it nears the Yellowstone River. Along the way irrigation needs pull from the river also causing its temperatures to warm.