Fishing boats on the Mekong river near Phnom Penh, Cambodia. Heng Chivoan
The Mekong River in some parts of the region including Thailand and Laos has taken on a blue-green hue due to the extremely low flows, according to the Mekong River Commission (MRC).
In a press release issued on Monday, the MRC said its preliminary analysis showed the slow drop in river sediments and the presence of algae on the sand and bedrock river bottom are among the possible causes.
So Nam, the MRC secretariat’s chief environment management officer who led the analysis, said the aquamarine hue is likely to occur elsewhere, bringing possible risks including change in river productivity and reduced productivity of aquatic biodiversity due to high water clarity.
“The blue-green water phenomenon is likely to spread to other stretches of the Mekong River where low flows are encountered. The issues of low flows and sedimentation could lead to adverse impacts that have been well-quantified in the MRC Council Study,” he said.
He said the phenomenon could deplete foods for insects and small fishes, which translate into lower fish catches for the local communities.
Nam told The Post on Tuesday that a recent MRC analysis had found no trace of the hue in Cambodia.
He said its routine monitoring of water quality in the Mekong River and its tributaries at 48 stations – 17 in the mainstream and 31 in tributaries, five of which are in the Bassac river – had indicated that the Mekong and Bassac water is still of good quality.
“But we will keep monitoring the situation in [Cambodia] and other three member states,” he said.
He said the MRC was taking the issue seriously and working with the National Mekong Committee to check the water quality in Thailand’s Nakhon Phanom and Laos’ Thakhek areas to see if the water was safe.
“Once the water is tested and results are out, we will provide an update to the public. We will constantly monitor the situation at other stretches of the river and the quality of water during this critical time.
“If any similar incident occurs, we will conduct the test and make the results available publicly,” he said.
Te Navuth, the permanent vice-chairman of the Cambodia National Mekong Committee, could not be reached for comment on Tuesday.
Citing its analysis, the MRC said high water clarity caused by the phenomenon could result in algal bloom, which leads to high levels of dissolved oxygen during the day but very low levels at night. That, it said, could affect the lives of different fish.
It stressed that if water clarity remains high, the algae could change from green to blue-green, producing toxic substances that can harm animals.
While noting that such conditions were unlikely to occur in the main river, Nam urged people to take extra caution.
“The conditions are restricted to backwaters, but people should be careful watering their animals if the water is very green,” he said.
Nam pointed out that the present blue-green conditions in the Mekong could continue until flows in the river increase at the beginning of the next flood season in May.
The conditions, he said, may recover if large volumes of water were released from the reservoirs in the Upper Mekong (Lancang) dam and tributary dams to mobilise sediments.
