The Waihemo / Shag River is located in Otago in the South Island of New Zealand. It rises in the Kakanui Range, flowing southeast for , or before reaching the Pacific Ocean on the south side of Shag Point / Matakaea, east of Palmerston.
In 1985, the name of the river was gazetted by Land Information New Zealand as Shag River (Waihemo). In August 2021, the name was officially amended to Waihemo / Shag River.