The Guide River is a river in the Marlborough Region of New Zealand. It starts near Barefell Pass on the eastern side of the Rachel Range and flows south-east to join the Acheron River, which joins the Clarence River and eventually drains into the Pacific Ocean.The river was discovered by Sir Frederick Weld and his station manager in 1850, who named it because it guided them from the Barefell Pass to the Acheron River (which they misidentified as the Clarence River).