The water of the Brahmaputra river has become unsuitable for daily use after an “unusual phenomenon” of excessive turbidity and change in colour, the Assam government found after tests, The Indian Express reported. The government of Arunachal Pradesh had made similar findings last month, after the water of the Siang river turned black in the last two months.

The Siang river is the main tributary of the Brahmaputra and connects it to the Yarlung Tsangpo, as the river is called in Tibet. China has denied reports that it was constructing dams or tunnels in its territory to contaminate the river downstream, the Hindustan Times reported.

The Assam government has sent samples for testing to the Indian Institute of Chemical Technology in Hyderabad and the Indian Institute of Technology in Guwahati.

People living near the river’s banks have said the water is unfit for consumption, PTI reported.

The turbidity of water samples collected from Mainjanghat, Bogibeelghat and Jahajghat areas were 296 NTU, 404 NTU and 162 NTU, the government said. NTU, which means “Nephelometric Turbidity Unit”, measures the concentration of suspended particulates in a liquid. Permissible turbidity for potable water is 5.

Assam Water Resources Minister Kesab Mahanta has urged Union Water Resources Minister Nitin Gadkari to order a detailed report on the actual cause of the “unusual development” in the river and to involve the Central Water Commission, a government release said.

On Friday, the state’s Health Minister Himanta Biswa Sarma had said that the construction of a dam or an accident in China had caused the Brahmaputra’s water in Assam to have the “abnormal deviations”, and contaminated it with cement particles.