The Ma River is a river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 in Asia

Asia

Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

, originating in northwestern 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 –...

. It runs for 400 km through Vietnam, Laos

Laos

Laos Lao: ສາທາລະນະລັດ ປະຊາທິປະໄຕ ປະຊາຊົນລາວ Sathalanalat Paxathipatai Paxaxon Lao, officially the Lao People's Democratic Republic, is a landlocked country in Southeast Asia, bordered by Burma and China to the northwest, Vietnam to the east, Cambodia to the south and Thailand to the west...

, and then back through Vietnam, meeting the sea at the Gulf of Tonkin

Gulf of Tonkin

The Gulf of Tonkin is an arm of the South China Sea, lying off the coast of northeastern Vietnam.-Etymology:The name Tonkin, written "東京" in Hán tự and Đông Kinh in romanised Vietnamese, means "Eastern Capital", and is the former toponym for Hanoi, the capital of Vietnam...

.

The largest tributaries of the Ma River are the Chu River

Nam Sam River

Chu River or Nam Sam River is the largest tributary of Ma River. It originates from Houa peak at 2062 m near Sam Neua town, Houaphan Province in Eastern Laos and travels eastern to meander through Nghe An and Thanh Hoa Provinces of Vietnam...

 (or the Nam Sam River as it is called in Laos), the Bưởi River, and the Cầu Chày River. All of them join the Ma River in Thanh Hoa Province in North Central Vietnam.

The Ma River creates the Ma River Delta (also called the Thanh Hoa Delta), the third largest in Vietnam.

The Ma River Delta used to be near Vietnam's southern frontier. It was the center of Cuu-Chan, the southern of the Vietnam's two prefectures under the rule of the Nanyue

Nanyue

Nanyue was an ancient kingdom that consisted of parts of the modern Chinese provinces of Guangdong, Guangxi, and Yunnan and northern Vietnam. Nanyue was established in 204 BC at the final collapse of the Qin Dynasty by Zhao Tuo, who was the military commander of Nanhai Commandery at the time, and...

in the 2nd century BC.