CHIANG RAI – The Provincial Administration is still watching water quality in the Kok, Sai, Ruak, and Mekong rivers closely after repeated tests found arsenic, lead, and manganese above standard limits at some points. The main concern now is not only river water, but also tap water safety, fish consumption, daily use, and long-term health risks.
Key Takeaways
- Tests found arsenic above the legal limit in parts of the Kok, Sai, and Ruak rivers, while the Mekong passed in the latest round.
- Officials said treated tap water in monitored areas still meets standards and can be used for daily life.
- Boiling river water does not remove heavy metals, so untreated natural water should not be used for drinking or cooking.
On June 16, 2026, Chiang Rai Province brought together government agencies, academics, civil groups, and the media for a public academic forum titled “One Year of the Kok and Mekong Rivers, Global Lessons, Real Conditions, Toxicology, and the Future of Food Crops.” The meeting took place at Chiang Rai Provincial Hall. It was designed to clear up confusion, explain the science, and set a long-term monitoring plan.
A key message from the forum was simple. Treated tap water that has gone through production and testing is still safe for normal use. Raw water from natural sources still needs treatment before use, especially in places where heavy metals have been found above the standard.
Public concern grows as water pollution data is shared
Cross-border water pollution has stayed in the spotlight after reports found contamination in rivers flowing from upstream areas into Thailand. People near the rivers worry about more than water quality. They also worry about fish, crops, and the health of their families.
One test result alone cannot explain the full picture. Water quality changes with the season, rainfall, water levels, sediment flow, and sampling location. A reading from one point should not be used to judge the whole river.
That is why the public needs clear details, such as which site was tested, which substance was found, how much was detected, and what the water is used for. A simple statement that arsenic was found above the limit can cause fear. A fuller explanation helps people understand the real risk.
Fish lesions in Kae fish are not cancer, but the ecosystem still needs attention.
One topic that drew strong interest was the case of Kae fish with bumps or lesions on their bodies. Some people feared cancer or a buildup of cancer-causing substances.
Research presented by Prof. Danny D. Reible of Texas Tech University in the United States said the condition was not cancer. The findings pointed to parasitic infection and secondary bacterial infection, confirmed through necropsy and blood testing.
That does not mean the river system is healthy. Kae fish live near the riverbed and spend time close to sediment. If fish are getting sick, it may mean the water environment is changing and making them more vulnerable to infection.
Bottom-dwelling fish are often a warning sign. Even if the wounds are not cancerous, scientists still need to check whether the sediment contains contaminants, whether fish diversity is falling, and whether deformities are becoming more common.
For that reason, academics urged officials to track water, sediment, aquatic animals, and biodiversity together. Heavy metals may stay low in the water but build up in sediment or in fish tissue.
Kok River shows arsenic above standard at several points
The Pollution Control Department released results from Surface Water Quality Monitoring Round 19, based on samples collected from May 19 to 22, 2026. The survey covered 22 sites on the Kok, Sai, Ruak, and Mekong rivers.
Most heavy metals, including cadmium, copper, nickel, chromium, zinc, and mercury, were still within standards. However, arsenic went above the surface water standard of 0.010 milligrams per liter at several sites.
The Kok River had arsenic above the limit at four points. These were:
- Tha Ton Bridge in Chiang Mai, 0.012 mg/L
- Mifamphan Kok River Bridge to Tha Ton, 0.013 mg/L
- Mifamphan Mae Yao to Doi Hang Bridge in Chiang Rai, 0.013 mg/L
- A bridge over the Kok River in Chiang Rai, 0.011 mg/L
The levels were not the same at every site, so the river needs ongoing monitoring. Rainstorms, floods, and falling water levels can move sediment and change contamination levels.
Sai River shows arsenic, lead, and manganese at some sites
The Sai River needs extra attention because some samples contained more than one metal above the standard.
- At Ban Hua Fai in Mae Sai District, tests found arsenic at 0.041 mg/L and lead at 0.056 mg/L. The lead standard is 0.050 mg/L.
- At the Second Thai-Lao Friendship Bridge over the Sai River, tests found arsenic at 0.037 mg/L and lead at 0.052 mg/L.
- At Ban Pa Sang Ngam in Ko Chang Subdistrict, tests found arsenic at 0.039 mg/L, lead at 0.056 mg/L, and manganese at 1.40 mg/L. The manganese standard is 1.00 mg/L.
These numbers mean the Sai River area needs strict monitoring, especially for direct use of natural water, dredging work, and sediment handling after floods. If contaminated sediment spreads into homes or farmland, the impact can last after the floodwater is gone.
At the same time, security agencies, Chiang Rai Province, and local governments have been repairing a semi-permanent flood barrier along the Sai River. The work is more than 60 percent complete. Flood control and pollution control need to move together, because floodwater can carry contaminated sediment into homes and fields.
The Ruak River still needs watching, while the Mekong passed this round
The Ruak River had arsenic above the standard at two points. One was the Ko Chang water pumping station of the Provincial Waterworks Authority, which tested at 0.020 mg/L. The other was in Wiang Subdistrict, Chiang Saen District, which tested at 0.014 mg/L.
The Mekong River, in the same round, did not show arsenic or other heavy metals above the standard. That shows the situation is different from river to river, and it should not be treated as one uniform problem across northern Thailand.
Even so, one clean round does not mean the water will stay safe all the time. Water quality can shift with river flow and sediment movement. Each report should list the sample date, location, and type of sample clearly.
Natural water and tap water are not the same thing
Many people still confuse river water with tap water. River water is raw water, which has not gone through treatment. It can contain sediment, germs, and contaminants from nature or human activity.
Tap water is different. It goes through settling, filtration, disinfection, and quality checks before it reaches homes.
According to Nakorn Chiang Rai, the Provincial Waterworks Authority said tap water produced and supplied in monitored areas still meets standards and can be used for normal consumption. The agency also set aside more than 9.25 million baht to test for heavy metals and other contaminants and to improve water production systems.
People do not need to panic or stop using tap water if test results still meet standards. They should, however, keep an eye on new notices, especially during floods or when the raw water source changes.
Water from rivers, ponds, or other surface sources should not be drunk or used for cooking without treatment, even if it looks clear and has no smell. Heavy metals cannot be seen with the naked eye.
Boiling water does not remove heavy metals.s
Dr. Yutthapong Thongphop, a lecturer at the Faculty of Medical Science, Naresuan University, said boiling water cannot remove arsenic or lead. Heavy metals do not disappear when water boils, and as water evaporates, the remaining contaminants can become more concentrated.
Households that must use natural water should use a filtration system made to remove heavy metals. The filter media also needs regular checks and replacement on schedule. A filter that is installed but not maintained can lose effectiveness and may even collect more contaminants inside the system.
People should choose tap water or bottled drinking water that is approved for drinking and cooking. If natural water is used for washing or other non-drinking tasks, follow local guidance.
Arsenic and lead can build up over time
Scientists at the forum said arsenic and lead can build up in the skin, hair, lungs, liver, and kidneys. They can also affect the nervous system, heart, and blood vessels. The biggest risk often comes from repeated exposure over five to ten years, not from one short exposure.
Warning signs can include dark spots on the skin, numbness in the hands and feet, weakness, nausea, vomiting, and stomach pain. Still, people should not self-diagnose arsenic exposure, because these symptoms can come from many other conditions. A doctor needs to check the full history, including water use, food, work, and exposure time.
Groups that need extra care include young children, pregnant women, older adults, people with chronic illness, fishers, and anyone who often touches river water or sediment. Chiang Rai should keep health monitoring in these risk areas ongoing, instead of waiting for many people to get sick.
Fish meat mostly meets standards, but organ meat is a concern
The forum said that over about one year, only one fish meat sample went above the standard. Fish organs were a different story, with about 30 percent of samples above the limit. Organs such as the liver and kidneys filter and store substances, so they often carry more heavy metals than fish flesh.
Because of that, academics recommend avoiding fish organs from monitored areas and choosing fish from sources that can be traced. At the same time, this does not mean every fish in the river is contaminated or that all fish from Chiang Rai are unsafe.
Fishery agencies should publish results with the fish species, catch site, sample size, and date. That gives residents and businesses a fair way to judge risk. Broad statements can hurt fishers, restaurants, and local sellers in places where samples still meet standards.
For rice cooking, academics suggested washing rice several times, or boiling it for about five minutes and discarding the first water before continuing to cook. This may reduce some arsenic, but clean water is still needed. If the water itself is contaminated, the rice can absorb more instead.
Online database and QR code tools are on the way.
The research team plans to build a website and a QR code system so the public can check water quality, sediment data, and contaminants in aquatic animals more easily. The team also plans to collect samples from water between sediment layers in July 202, and to track fish diversity and food security impacts.
The system should show information in a format people can understand, such as a map of sampling points, the date collected, test values, standard limits, and guidance for each area. It should also separate raw water, tap water, sediment, and aquatic animal results, since each one uses different standards.
Regular disclosure helps reduce rumors and build trust more than a simple “safe” or “unsafe” label. People should be able to look back and see whether a site is improving or getting worse, and what actions the agencies took after a test exceeded the limit.
Chiang Rai is moving on with flood plans and long-term water management
Along with pollution concerns, Chiang Rai is also preparing for the 2026 rainy season. The provincial governor has told local governments to lead in three phases: before flooding, during the event, and after the water recedes.
The main steps include dredging canals, clearing blockages, checking pumps, running evacuation drills, setting up emergency operations centers, and speeding up compensation after disasters. Mae Sai is a top priority because it was hit hard by the 2024 floods.
Chiang Rai has also received a five-year water management plan and four pilot projects. These include a flood damage map for urban areas, a local flood warning system, upgrades to weirs to improve water supply, and an arsenic removal system for drinking and household water.
Connecting flood planning with pollution monitoring matters. Floodwater does not carry only water and mud. It can also spread contaminated sediment into homes, farms, and community water sources.
