The Søo, also known as the Søa, is a river in the municipality of Hemne in Sør-Trøndelag County, Norway. It originates at Lake Søo (Søvatnet) in the municipality of Orkdal (280 meters or 920 feet) and further from Lake Vassli (Vasslivatnet; 280–260 meters or 920–850 feet, depending on the regulation).