river in southern Alberta, Canada, one of the major headstreams of the South Saskatchewan River. Rising in the Canadian Rocky Mountains from several sources, it flows eastward through Lethbridge, past Taber Provincial Park, and joins the Bow River to form the South Saskatchewan River, 44 miles (70 km) west of Medicine Hat. The Oldman, 250 miles (402 km) long from the head of the Crowsnest River (its chief headstream), was an important coal transport route in the 19th century. The valley of the river and its three main feeder streams—the Belly, St. Mary, and Little Bow—now form a major irrigation district of more than 1,000,000 acres (400,000 hectares). The 1991 construction of a dam just upstream from Pincher Creek was strongly opposed by environmental groups. The dam was built to increase irrigation and urban water supplies.