TOI photos.

GUWAHATI: The crystal clear waters of the Siang river , considered the lifeline of northern Arunachal Pradesh for centuries, has suddenly turned dark black triggering panic in the frontier state.The East Siang district authorities have pressed the alarm bell as the water of the river, containing large volumes of heavy slag, is no longer fit for consumption. "The water can't be used for any purpose because it contains a cement-like thick material. A lot of fish died one-and-half months ago," said East Siang district deputy commissioner Tamyo Tatak.He added, "In the last monsoon season, the river turned dark and we thought that it was because of mud being carried by the river. The rainy season is long over but the river water is still black. From November to February, the water is crystal clear and pure. Even my grandfather has never seen or heard of such a thing happening to the waters of the Siang."Tatak said water samples have been collected by the central water commission and China is the primary suspect."It seems that some major cement work is on in the upper reaches of the river in China ... may be China is carrying out some deep water boring work. What else could be the reason for such a big river, which becomes the Brahmaputra, remaining black in colour for nearly two months," Tatak said. The Siang is the principal constituent river of the Brahmaputra and flows for 1,600 km through southern Tibet as the Yarlung Tsangpo or Yarlung Zangbo before entering India.Siang is also known as Dihang in India, which joins the Lohit after flowing for 230 km. The Dibang joins at about 35 km downstream of Pasighat in East Siang district to form the Brahmaputra. Tatak said he has submitted an independent report to the Arunachal government describing the situation.India's worst fears are from Chinese plans to dig a 1000-km tunnel, the world's longest, to divert the Yarlung Tsangpo river from Tibet to Taklimakan Desert in Xinjiang. However, China has denied having any such plans.Read this story in Bengali