The Central Inland Fisheries Research Institute (CIFRI) has detected high turbidity in the waters of the Siang where investigation for chemicals and biological ingredients is under way. A team of researchers from the institute, who had recently visited the upper reaches of the Brahmaputra and Siang rivers, said change in water content has reduced the fish population at an alarming rate. According to the Brahmaputra Water Investigation Report published recently by the institute, more than 1,000 formazin nephelometric units (FNU) have been found with transparency of about 2 to 4cm. In September – before the report on Brahmaputra’s waters – the institute had conducted a survey in the Siang where transparency of water was around 15cm. An official with the institute said in the earlier study, general turbidity was not investigated and so they could not say the standard level. But the current level might be below danger level, they felt. In September, the rate of total dissolved solid was under the range of 100 to 150 milligram per litre. Now itis 200 milligram per litre. The total dissolved oxygen rate was 7.9, which is the same as now. “Because of extensive floods every year, Assam reels under water for many days. So the capacity to tolerate high turbidity also increases for the fishes of the Brahmaputra and other rivers. But if this condition continues for many days, it will harm fishes ,” the principal scientist and acting head of Guwahati-based CIFRI Northeast Regional Centre, B.K. Bhattacharjya, said. Simanksu Borah, another scientist with the institute, who was also a member of the team that recently had visited the Siang, said: “Due to high turbidity this time, no migratory fish came to our notice. Even local fishermen said they could not catch migratory fishes in this season. Generally due to low temperature in the upper part of the river, fishes such as mahseer swim downstream. But this year the fish may have opted for other tributaries.” The CIFRI team had collected fish and water samples. The institute has also sent some samples to Jorhat-based regional centre of National Bureau of Soil Survey and Land Use Planning (NBSSLUP). Some samples were also sent to the Calcutta-based laboratory of the CIFRI. “We have got the sample from the CIFRI and started an investigation,” a scientist with NBSSLUP, Sanjay Kumar Ray, said.