The Sagavanirktok River or Sag River (Iñupiaq: Saġvaaniqtuuq) is a stream in the North Slope Borough of the U.S. state of Alaska. It is about 180 mi long and originates on the north slope of the Brooks Range, flowing north to the Beaufort Sea near Prudhoe Bay. The Trans-Alaska Pipeline System and Dalton Highway roughly parallel it from Atigun Pass to Deadhorse. A glaciation happened approximately at the same time as the Illinoian Stage of central North America at the Sagavanirktok River.