The Siang river in Arunachal Pradesh started showing signs of turbidity in October. Two months later, the river’s changing colour, now visibly black, remains a mystery. The Siang is the main tributary of the Yarlung Tsangpo, as the Brahmaputra is called in Tibet, where it originates.

So far, explanations have ranged from possible construction activity on the Chinese side to natural tectonic occurrences. But with no consensus, or official word, on the matter, this is merely speculation. Meanwhile, there is alarm in Assam and Arunachal Pradesh, where thousands of livelihoods depend on the river.

Tunnel theory

The darkening of the Brahmaputra came to national attention earlier this month when Ninong Ering, a Congress MP from Arunachal, requested Prime Minister Narendra Modi to take up the matter with China. In his letter, Ering attributed the phenomenon to Chinese construction activity, citing a news report to support his claim. The report, published on October 30, detailed China’s purported plan to build a tunnel to divert water from the Yarlung Tsangpo in Southern Tibet to Taklamakan desert in Xinjiang province. The Chinese government has denied it has such a plan, calling the report false.

Meanwhile, a sample tested by Arunachal’s Public Health Engineering department confirmed the turbidity of the Siang’s waters was several times higher than the permissible limit. Soon, reports of fish and animals dying from the polluted waters started to emerge from the Siang Valley. There was a public outcry, forcing Chief Minister Pema Khandu to ask the central government to take the matter up with Beijing.

China, though, maintained that it had nothing to do with the muddying of the waters. In a report in the state-owned The Global Times, Chinese analysts were quoted as saying that “India should not point its finger at China”. The report, which referred to Arunachal Pradesh as South Tibet, reasoned that China would not pollute its “local environment”.

Earthquake explanation

Finally, on December 4, Union Minister of State for Water Resources, River Development and Ganga Rejuvenation Arjun Ram Meghwal told reporters the reason for the unusual phenomenon could be natural. He said a preliminary study conducted by the Central Water Commission – responsible for the control, conservation and utilisation of water resources in the country – suggested the Siang’s waters had turned black after an earthquake in Tibet. An earthquake measuring 6.3 on the Richter scale had struck the Nyingchi region of Tibet on November 18.

Meghwal’s explanation, however, did little to allay fears in the Siang Valley. While Ering termed the contention absurd, the All Arunachal Pradesh Students’ Union said the minister’s response reflected Delhi’s “callous attitude” towards the river.

On December 7, Minister of State for Home Affairs Kiren Rijiju, who is from Arunachal, tweeted that the central government was “continuously tracking and assessing” the river.

Assam agitation

By now, the waters of the Brahmaputra downstream in Assam were also turning turbid. People living along its middle reaches complained that the muddy waters had started to adversely affect their livelihood.

Although the state’s Water Resources Minister Keshab Mahanta claimed a government testing facility had found no harmful chemicals and that the blackening of the waters was probably the result of a natural process, not everyone was convinced. Over the last week, several local organisations have organised protests, demanding action from the government. On Monday, over 300 students in Guwahati formed a human chain, exhorting the Centre to save the Brahmaputra river from contamination.

New twist

As the theory seemed to be shifting from the “Chinese hand” to a geological occurrence, a report on the news website The Print on Wednesday again put forth the former as the likely reason behind the blackening of the Siang’s waters. The report, written by a former officer of the Indian Army, cites satellite imagery procured from a commercial American vendor to contend that China is diverting the river into an underground tunnel. The blackness of the waters, the report states, could be because of polymer resin adhesives being sprayed around the tunnel as dust suppressant.

However, a test conducted earlier by the North Eastern Regional Institute of Water and Land Management, Assam, had not found any such chemicals in the river’s waters. The turbidity, the institute’s report said, was caused by excessive soil in the water.

Following The Print’s report, the Chinese government on Wednesday again refuted the allegation that it was diverting the Brahmaputra. “I have never heard of the project mentioned by the Indian side,” the Chinese foreign ministry said in a statement. “It is hoped that the Indian side will not conduct unfounded speculation and reports.”

India’s Foreign Minister Sushma Swaraj, meanwhile, is reported to have approached China to carry out a “pragmatic and exhaustive” study to ascertain the reasons behind the blackening of the Brahmaputra.