The Mekong River, often called the “Mother River” of Southeast Asia, is one of the world’s largest and most biologically diverse transboundary waterways. Flowing through six countries, it supports the food security, livelihoods, and culture of over 60 million people. The river’s immense economic and geographical significance, particularly in the lower basin and the vast Mekong Delta, is now threatened by extensive pollution. Scientific monitoring confirms this vital ecosystem faces complex contamination challenges that compromise its water quality and ecological integrity. Pollutants originate from various sources across the basin, creating a serious public health and environmental crisis.
The Current State of Contamination
The water and sediments of the Mekong River system contain a mix of contaminants resulting from decades of human activity. Microplastics are a pervasive pollutant, found in both the surface water and the bottom sediment, particularly concentrated in the lower reaches. Surveys have measured microplastic concentrations in the Mekong Delta as high as 64 items per cubic meter in key areas like Can Tho. These microplastics are predominantly fibers, suggesting sources like textile effluent and laundry discharge, with common polymers including Polyethylene Terephthalate (PET).
Heavy metals represent another category of contamination, accumulating in riverbed sediment and aquatic life. Analyses of river sediments show increasing concentrations of metals like zinc, copper, lead, and arsenic over the last decade. While some levels may adhere to national standards, they often exceed international environmental thresholds in the lower basin. These metals, along with Persistent Organic Pollutants (POPs), concentrate in sediment hotspots.
Biological and nutrient contamination is pronounced in densely populated areas. Monitoring reveals high levels of nitrogen and phosphorus, which are primary nutrients that fuel eutrophication and degrade water quality. The presence of Escherichia coli (E. coli), a key indicator of fecal contamination, is widespread. These microbial pollutants are often flushed into the river during the annual rainy season, posing an immediate public health risk.
Primary Sources of Pollution
The contamination in the river is directly linked to three major human activities: inadequate waste management, intensive agriculture, and resource extraction. Rapid urbanization and industrial growth have severely strained existing wastewater treatment infrastructure. Many industrial zones and urban centers discharge municipal sewage and untreated industrial effluent directly into tributaries and the mainstream. In the Mekong Delta, only a small percentage of industrial zone wastewater is treated, allowing harmful chemicals from industries like textile and seafood processing to enter the water.
Unregulated mining operations, particularly in the upper tributaries of Laos, Myanmar, and Cambodia, are a major source of heavy metal contamination. These activities release toxic substances like arsenic, mercury, cyanide, and lead into the river system. Elevated arsenic levels have been recorded in tributaries, sometimes exceeding the safe limit for drinking water, which then flows downstream.
Intensive agricultural practices throughout the basin contribute non-point source pollution through runoff. The overuse of agrochemicals is widespread; estimates suggest that more than 140,000 tons of fertilizer are unnecessarily applied each year in the Mekong Delta alone. This excess nitrogen and phosphorus washes into the river, contributing to eutrophication. Pesticide and herbicide residues, including the restricted insecticide Cypermethrin, also enter the river from agricultural fields, particularly following heavy monsoon rains.
The widespread construction of dams also exacerbates pollution issues by altering the river’s natural processes. Dams trap a significant portion of the river’s sediment load, which historically carried vital nutrients and helped dilute pollutants downstream. This reduction in sediment, which could be as high as 94% if all planned projects are completed, reduces the river’s natural capacity to flush and process contaminants. The resulting clearer water column and lower flow rates increase the relative concentration of pollutants.
Environmental and Human Health Impacts
The pollution crisis has profound consequences for the Mekong’s biodiversity and the human communities that rely on it. Environmentally, the combination of habitat degradation and toxic contamination is pushing many endemic species toward collapse. At least 19% of the nearly 400 assessed Mekong fish species are now threatened with extinction. The inland fishery, the world’s largest, has seen its harvests decline by 25–30% between 2015 and 2020. Fish populations in key areas, such as Cambodia’s Tonle Sap Lake, have experienced an estimated 88% collapse in size in recent years.
The bioaccumulation of toxins is a primary mechanism driving this environmental decline. Heavy metals like lead and cadmium are absorbed by aquatic organisms, concentrating in the fatty tissues and organs of fish, amphibians, and water birds. This bioaccumulation causes organ damage and physiological stress, disrupting the entire food web. Persistent Organic Pollutants (POPs), such as DDT and endosulfan, are also found in high concentrations in the fatty tissues of animals in wetland hotspots, impacting their reproductive and neurological health.
For the human population, health risks stem from acute exposure to pathogens and chronic exposure to chemical contaminants. Fecal pathogens, indicated by high E. coli levels, are linked to waterborne diseases affecting communities relying on the river for drinking and sanitation. A more insidious threat is the long-term ingestion of heavy metals and POPs through the diet and water supply.
Arsenic exposure is a pervasive problem, with high intake levels from contaminated groundwater and the consumption of arsenic-enriched rice and fish in the delta. This chronic exposure increases the risk of developing non-cancerous skin lesions and is linked to an elevated incidence of lung cancer. The consumption of contaminated fish poses a disproportionate risk to vulnerable groups. Non-carcinogenic and carcinogenic health effects are estimated to be nearly six times higher for children than for adults in some affected regions. Exposure to POPs is also associated with long-term effects on the nervous and endocrine systems, and an increased risk of chronic ailments like cardiovascular disease and diabetes.