About 3,50,000 litres of furnace oil spilled from an oil tanker called OT Southern Star 7, after it was hit from behind by an empty cargo ship, Total.
Sources said the oil might have spread over 50 km on the waters of Shela where the tanker sank, and Pashur rivers.
Authorities in Dhaka have ordered an intensified campaign to remove oil from the waters as it had spread quickly through a wide network of rivers and channels in and around the forest.
Forest officials and environment experts are deeply worried because as the oil spill spreads, it threatens the water bodies' wildlife, especially dolphins. Experts say the spill will cause massive ecological disaster in the biggest mangrove forest in the world.
Pradeep Vyas, Additional Principal Chief Conservator of Forests and Director, Sunderbans Biosphere Reserve, told NDTV, "Border camps have been alerted for any sign of spillage. So far there has been no impact on Indian side as the spill location far from Indian side of Sunderbans... This is a very serious incident. There is a dolphin sanctuary near spill site."
The Sunderbans forest, which cover 26,000 square kilometres in India and Bangladesh, is the habitat of famous Royal Bengal Tigers. It is also a Unesco Heritage site.
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