The St. Mary River is a river located in the northwestern region of the United States and southwestern Canada. It flows from the eastern slopes of the Rocky Mountains in Montana and travels northward into Alberta, where it eventually joins the Oldman River. The river is approximately 120 miles long and is known for its scenic beauty and recreational opportunities. The St. Mary River is an important water source for agriculture and irrigation in the surrounding areas. It also supports various wildlife habitats and is popular for activities such as fishing, kayaking, and hiking along its banks. The river plays a significant role in the local ecosystem and economy.