Bangladesh Inland Water Transport Authority (BIWTA) on Monday once again imposed a ban on all types of water vessels through the Shela River in the world’s largest mangrove forest and a listed heritage site – the Sundarbans.Saidul Islam, divisional forest officer of the Sundarban’s Chandpai range confirmed the matter.In December 2014, an oil tanker sank in the Shela River spilling huge quantity of oil that tainted the water with a black hue for days. The oil was found on barks of trees and on the soil for months.Later, the government suspended Shela river route for a few days before reopening it again in January.The Shela river route was permitted by the BIWTA in April 2011 as an alternative route to the Mongla-Ghashiakhali channel.