High levels of chemical poisons have been found in the Mvoti River near KwaDukuza/Stanger, which has led to an immediate ban on fishing, swimming or drinking water near the Sappi paper mill.
The multinational pulp and paper company has also advised fishermen not to eat any fish or other marine creatures from the immediate vicinity of the Mvoti River mouth until further tests have been conducted.
Sappi has shut down its pulping operation at Stanger and has halted the chlorine bleaching process which caused the toxic chemical pollution. For the time being, the mill is importing pulp from other mills.
The company, which owns paper mills on three continents, said "higher than advisable levels" of dioxins, furans and other organo-chlorinated compounds had been found in samples of fish and river mud in the Mvoti River and in a small stream south of the Sappi mill.
Toxicology expert Dr Willie van Niekerk had compiled a report on the problem, but Sappi declined to release a copy, saying that the findings were still "very preliminary".
The full list of compounds found in the river has also not been released to the media.
However, Mill Manager John Rowland and Sappi spokesperson Mark Albon said that some of the sample measurements were "about four to five times higher" than World Health Organisation and European Union health guidelines.
The company acknowledged that some of these compounds had the potential to cause cancer and endocrine system health problems in humans and animals, depending on the dose and duration of exposure.
Dioxin-type compounds are a highly toxic chemical family, and are commonly associated with chlorine-based pollutants, such as the Agent Orange herbicide, which was sprayed over Vietnam.
In the early 1980s, the town of Times Beach, Missouri, was even evacuated after roads were sprayed with dioxin-contaminated waste oil.
Although the toxicity of dioxin-like chemicals varies considerably, the most dangerous forms have been known to affect the immune and reproductive systems as well as brain development, and cause liver damage, birth defects and cancer.
Laboratory animal experiments have also revealed changes in hormone levels, lower sperm counts and abnormalities in sexual organs.
The highest pollution readings near the Sappi Stanger mill were found in river sediments (300-400 nanograms per kilogram), while fish samples showed levels of between 46ng/kg and 21ng/kg.
Albon suggested that people eating contaminated fish from the Mvoti River would have to be exposed "for about 70 years to get a disease", but the company had decided to take a cautious approach and warn people not to expose themselves to danger by eating river fish, swimming in or collecting drinking water between the mill and the river mouth.
The most serious risk was eating fish, but swimming in or drinking the water was not recommended, he said.
Dioxin safety guidelines are much more stringent in the United States, where the Mvoti levels would be viewed as considerably over the recommended limits.
Albon said the toxic pollution samples had been collected late last year and sent to Germany for laboratory analysis.
The tests results arrived back last month, and several government departments had been notified in late January.
Meetings had also been held with senior KwaDukuza municipal officials, farmers and other interest groups.
"From the information that we currently have, the risk to the community is likely to be very low, and very few people are likely to have been exposed directly.
"Sappi has initiated further scientific studies in order to more clearly understand the impact that these compounds may have on the environment, and to investigate their impact, if any, on people," Albon said.
He also confirmed that the company, which bought the mill in 1979, had never tested the river for dioxin-type pollution until late last year.
However, according to international health and environment activist Lois Marie Gibbs, the American pulp and paper industry had known about the likelihood of dioxin pollution from many of its mills since the mid 1980s.
In her book Dying from Dioxin, Gibbs said the industry signed secrecy agreements with the United States Environmental Protection Agency to suppress the disclosure of test results which showed that
dioxins were present in pulp/paper mill effluent across the country.
Albon said that, until last month, the Stanger mill had been the last Sappi operation in the country to use chlorine as a bleaching agent. He conceded that the current dioxin problem had probably existed for several years.
The nearby Sappi Tugela mill did not use chlorine as a bleaching agent, because it produced "brown", unbleached pulp.
Dr Timothy Fasheun, the provincial government Head of Pollution and Waste Management, said dioxin-type pollution was likely to persist in the Mvoti for at least eight years.
"The most important issue right now is to alert the community - especially fishermen - as these toxins build up over a period of time in the fatty tissues of animals," he said.
Lin Gravelet-Blondin, of the Department of Water Affairs, said: "I don't think it's a train smash or crisis, but it is a cause for concern, because the levels are high compared to European Union guidelines... but I'm not an expert on health issues."
He said he could not comment on the best way to rehabilitate the river, although attempts to dredge up contaminated silt were likely to create bigger problems.