High turbidity turning river Siang black: Lab reports

GUWAHATI: Laboratory tests results of samples of the dark waters of the Siang in Arunachal Pradesh have confirmed that high turbidity has made the principle constituent of the Brahmaputra a river of death for aquatic life besides rendering its water unfit for human consumption.

Deputy commissioner of East Siang district Tamyo Tatak told TOI that the colour of the river water is dark for nearly two months now. He added that chief minister Pema Khandu will visit Pasighat on Saturday to inspect the river himself.

The report of the state public health engineering (PHE) department, which had taken samples of the river water on November 27 to the laboratory, shows that Nephelometric Turbidity Unit (NTU), the measure of turbidity of water caused by concentration of suspended or dissolved particulate materials in water that scatter light making the water appear cloudy or murky, especially clay and silt, is 425 NTU, which is more than 400 times higher than the permissible limit of 5 NTU for drinking water.

According to a report of study of environmental impact by the state pollution control board, Siang's turbidity measure should have been between 12 and 15 NTU at this time of the year. Even in the monsoon season (September), Siang's turbidity is between 295 and 329 NTU which, too, clears up after a short time.

The PHE lab test report states, "A high turbidity level of more than 425 NTU, if exposed for a long period, may affect fish survivability as it leads to choking of gills resulting in death." The deputy commissioner confirmed that large number of fish have died in the last one month.

The lab result also shows a higher degree of iron content in Siang waters, 10 PPM (particles/million), against the permissible limit of just 0.1 to 2 ppm.
The Siang, which flows as Yarlung Tsangpo from southern Tibet, becomes the Brahmaputra after joining the Lohit river and several other tributaries just outside the boundary with Assam.