The Lainio River (Swedish: Lainioälven, Meankieli: Lainionjoki or Lainionväylä) is a river in Kiruna Municipality in the far north of Swedish Lapland. Its source is a mountain lake, Råstojaure (Meankieli: Rostujärvi), which lies along the border with Norway. 200 km from its source, the Lainio River flows into the Torne River, which eventually flows into the Gulf of Bothnia.