Son River or Troc River (lit. Lipstice River because its water is red in flooding season) is a tributary of Gianh River

Gianh River

The Gianh River is a river in the Quang Binh Province of Vietnam's North Central Coast . The river is 268 km in length.It was the border between ruling families during the partition of Vietnam following the Trịnh-Nguyễn War of the 17th century, serving to effectively divide the country between...

 in Quang Binh Province

Quang Binh Province

Quảng Bình , formerly Tiên Bình under the reign of Le Trung Hung of the Lê Dynasty, this province was renamed Quảng Bình in 1604) is a province in the North Central Coast of Vietnam....

, Bac Trung Bo

Bac Trung Bo

Bắc Trung Bộ is one of the regions of Vietnam. It consists of six provinces: Thanh Hóa, Nghệ An, Hà Tĩnh, Quảng Bình, Quảng Trị, Thừa Thiên-Huế...

, Vietnam

Vietnam

Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...

. 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... Son River makes confluence with Gianh River

Gianh River

The Gianh River is a river in the Quang Binh Province of Vietnam's North Central Coast . The river is 268 km in length.It was the border between ruling families during the partition of Vietnam following the Trịnh-Nguyễn War of the 17th century, serving to effectively divide the country between...

 near Ba Đồn town of Quang Trach

Quang Trach

Quảng Trạch is a district of Quang Binh province, in the North Central Coast of Vietnam. The district capital is Ba Đồn townlet. This district is divided into 34 commune-level subdivisions....

 District before emptying into South China Sea

South China Sea

The South China Sea is a marginal sea that is part of the Pacific Ocean, encompassing an area from the Singapore and Malacca Straits to the Strait of Taiwan of around...

. .