New reservoirs could produce toxic algae for 5 to 10 years.

Almost 10 years after villagers in northeast Cambodia first reported the Se San River smelled bad and was making them ill, Nordic experts have identified the problem: toxic blue-green algae in a large hydro reservoir in Vietnam, about 70 kilometres upstream from the Cambodia-Vietnam border.

According to an environmental impact assessment prepared by the Norwegian Institute for Water Research and Nordic hydro consultants, SWECO Groner: “The analyses confirmed that there are strains of toxin-producing blue green algae present in [Yali] Reservoir” and that the algae produces “exactly the same symptoms” reported by downstream Cambodians.

Cyanobacteria is the scientific name for blue-green algae or “pond scum” which releases several types of toxins that can attack the liver (hepatotoxin) or the nervous system (neurotoxins) when ingested or can simply cause itchiness after bathing. Liver poisoning may take hours or days to appear and can cause abdominal pain, diarrhea and vomiting in humans and death in animals. In combination with other liver diseases such as hepatitis, the impact can be deadly.

Between 1998 and 2000, the US$1 billion Yali dam flooded 65 square kilometres of land and forest, creating ideal nutrient-rich conditions for the foul-smelling algae.

“It seems very likely,” the experts conclude, “that during the first 2-3 years [when the Yali reservoir was filling] there have been incidents with toxic blue green algae, which have [produced] water quality problems in Se San River in Ratanakiri . . . that caused or contributed to the health problems for animals and people during 2000.”

The symptoms experienced by people along the Se San in Ratanakiri province – headaches, dizziness, and respiratory problems – were likely caused by an algal neurotoxin called microcystin, the report says.

At least 28,000 people in northeast Cambodia rely directly on the Se San River for their drinking water, as well as for bathing, fishing, and watering livestock.

Testing done in the Yali reservoir and downstream at the end of the 2005 rainy season found concentrations of algal toxins that were too low to pose an immediate health threat. However, the report warns that algal blooms can spread within a few days and that higher concentrations are likely in the dry season.

The report recommends testing the Yali reservoir every 14 days in the dry season and warns that algal blooms could appear in new hydro reservoirs along the Se San River for 5 to 10 years after filling.

In China, toxic blue-green algae has infected two of China’s biggest lakes this year, forcing residents of Jiangsu province to turn off contaminated tap water supplies. The health scare has prompted government authorities to test the contaminated water on an hourly basis and instruct residents not to use the water until the toxins dissipate.

Earlier hydro studies financed by Canada, Norway and Sweden failed to warn Electricity of Vietnam about the health and environmental risks associated with its dam operations on the Se San River, a large Mekong tributary flowing from Vietnam’s central highlands through northeast
Cambodia.

In 2000, sudden water releases from the Yali dam killed more than 30 people in downstream Cambodia and swept away people’s boats, fishing gear, and crops. The dam’s owner, Electricity of Vietnam, has yet to provide compensation for these and other damages despite appeals from local residents and Cambodian officials. For more information and photos, contact:

Grainne Ryder
Policy Director
Probe International
Toronto, CANADA
Phone: 1 416 964 9223 ext 228
Email: GrainneRyder@nextcity.com

Probe International is a Toronto-based citizens group monitoring the environmental and economic effects of Canadian aid and companies in developing countries.