Son River or Troc River (Vietnamese: Sông Son or sông Tróc) (lit. Lipstice River because its water is red in flooding season) is a tributary of Gianh River in Quang Binh Province, Bac Trung Bo, Vietnam. This river runs in the territory of Quang Binh Province. The upstream of this river with the length of 7729 m runs underground in limestone mountains of Phong Nha-Ke Bang National Park..[1]. Son River makes confluence with Gianh River near Ba Đồn town of Quang Trach District before emptying into South China Sea. .[2]