The extreme seasonal variations in flow and the presence of rapids and waterfalls in the Mekong make navigation difficult, though the river remains a major trade route between Tibet and Southeast Asia.

Khon Pi Long is a series of rapids along a 1.6 km (1.0 mi) section of the Mekong River dividing Chiang Rai and Bokeo Province in Laos.

Downstream from the Golden Triangle, the river flows for a further 2,600 km (1,600 mi) through Laos, Thailand, and Cambodia before entering the South China Sea via a complex delta system in Vietnam.

The catchment here is steep and narrow with Soil erosion being a major problem and as a result of this, approximately 50% of the sediment in the river comes from the upper basin.

Only 14 have catchment areas that exceed 1,000 km2 (400 sq mi), yet the greatest amount of loss of forest cover in the entire river system per square kilometer has occurred in this region due to heavy unchecked demand for natural resources.

Locals are blaming low water on the newly constructed Xayaburi Dam, as it enters its test phase prior to the start of commercial operation in October 2019.

[4] Most large river systems that drain the interiors of continents, such as the Amazon, Congo, and Mississippi, have relatively simple dendritic tributary networks that resemble a branching tree.

[21] Typically, such patterns develop in basins with gentle slopes where the underlying geological structure is fairly homogeneous and stable, exerting little or no control on river morphology.

These complex drainage systems have developed in a setting where the underlying geological structure is heterogeneous and active, and is the major factor controlling the course of rivers and the landscapes they carve out.

[23] The elevation of the Tibetan Plateau during the Tertiary period was an important factor in the genesis of the south-west monsoon,[24] which is the dominant climatic control influencing the hydrology of the Mekong Basin.

Understanding the nature and timing of the elevation of Tibet (and the Central Highlands of Vietnam) therefore helps explain the provenance of sediment reaching the delta and the Tonle Sap Great Lake today.

[27] Sediments deposited in the Tonle Sap Great Lake about this time (7.9–7.3 ka) also show indications of marine influence, suggesting a connection to the South China Sea.

From 5.3 to 3.5 ka the delta advanced across a broad embayment formed between higher ground near the Cambodian border and uplands north of Ho Chi Minh City.

From around the time of the fall of the Khmer empire, the Mekong was the front line between the emergent states of Siam and Tonkin (North Vietnam), with Laos and Cambodia, then on the coast, torn between their influence.

The first systematic European exploration began with the French Mekong Expedition led by Ernest Doudard de Lagrée and Francis Garnier, which ascended the river from its mouth to Yunnan between 1866 and 1868.

During the wars in Indochina in the 1970s, a significant quantity of explosives (sometimes, entire barges loaded with military ordnance) sank in the Cambodian section of the Mekong (as well as in the country's other waterways).

[40] The biggest include three species of Probarbus barbs, which can grow up to 1.5 m (5 ft) and weigh 70 kg (150 lb),[41] the giant freshwater stingray (Himantura polylepis, syn.

The endangered Siamese crocodile (Crocodylus siamensis) occurs in small isolated pockets within the northern Cambodian and Laotian portions of the Mekong River.

The very flat Mekong delta area in Vietnam is thus prone to flooding, especially in the provinces of An Giang and Dong Thap (Đồng Tháp), near the Cambodian border.

[48] People living within the Mekong River system generate many other sources of food and income from what are often termed "other aquatic animals" (OAAs) such as freshwater crabs, shrimp, snakes, turtles, and frogs.

[49][50][54] They provide a principal form of income for numerous people and act as a safety net and coping strategy in times of poor agricultural harvests or other difficulties.

These mother vessels sail directly to Europe or the United States, which means that goods can be shipped internationally to and from Phnom Penh with only a single transshipment at Cai Mep.

The most important of these, which address the full length of the river, are:[4] In December 2016, the Thai cabinet of Prime Minister Prayut Chan-o-cha agreed "in principle" to a plan to dredge stretches of the Mekong and demolish rocky outcrops that are hindrances to easy navigation.

[60] On 4 February 2020, the Thai Cabinet voted to stop the project to blast and dredge 97 km (60 mi) of the river bed after Beijing failed to stump up the money for further surveys of the affected area.

The Third Thai–Lao Friendship Bridge opened for traffic on 11 November 2011, connecting Nakhon Phanom Province (Thailand) and Thakhek (Laos), as part of Asian Highway 3.

The Kizuna Bridge is in Cambodia, in the city of Kampong Cham, on the road linking Phnom Penh with the remote provinces of Ratanakiri and Mondolkiri, and Laos.

Another new bridge was built at Neak Leung on the Phnom Penh to Ho Chi Minh Highway 1 with Japanese government assistance, and opened in 2015.

[69] A growing number of academics, NGOs, and scientists have urged the international community and the Mekong River Commission to reduce the use of hydropower, giving concerns of long-term sustainability.

Some of them have urged an immediate moratorium on new construction of hydropower projects and a shift to solar and other forms of renewable energy, which are becoming more competitive and faster to install.

These impacts include river embankment instability, reduced supply of vital floodwater and sediments to floodplains, increased salinity levels and both the disturbance and displacement of various species.