At low tide, oil marks are clearly visible on the mangroves in the Sundarbans forest in Harbaria area, around 10 km away from the UNESCO World Heritage site where on 9th December an oil-tanker named Southern Star VII, carrying 350,000 litres of furnace oil was sunk in the river after it had been hit by a cargo vessel. The oil spill, which covered 20 km of waterways, is very threatening to the region's flora and fauna.