Given the task definition and input, reply with output. In this task, you are given a context paragraph, a question based on that and corresponding answer of a question. Your task is to generate supporting fact/knowledge from context paragraph which helps in answering a given question.

The Tongue River is a tributary of the Yellowstone River, approximately 265 mi (426 km) long, in the U.S. states of Wyoming and Montana. The Tongue rises in Wyoming in the Big Horn Mountains, flows through northern Wyoming and southeastern Montana and empties into the Yellowstone River at Miles City, Montana. Most of the course of the river is through the beautiful and varied landscapes of eastern Montana, including the Tongue River Canyon, the Tongue River breaks, the pine hills of southern Montana, and the buttes and grasslands that were formerly the home of vast migratory herds of American bison. The Tongue River watershed encompasses parts of the Cheyenne and Crow Reservations. The Headwaters lie on the Big Horn National Forest, and the watershed encompasses the Ashland Ranger District of the Custer National Forest. Question: The Tongue River Dam impounds a tributary that is approximately how many miles long? Answer: 265
The Tongue River is a tributary of the Yellowstone River, approximately 265 mi 426 km long, in the U.S. states of Wyoming and Montana.