A fisherman shows a Hilsha fish after catching it from Pasur River. Pasur River a big river in the Sundarbans area is an extension of the Rupsa River, South of Khulna. The Bhairab or the Rupsa flows further south and is renamed as Pasur near Chalna and falls into the Bay Of Bengal flowing to the right of Trikona and Dubla islands. South of Mongla upazila the river flows into the Sundarbans. Mongla, Khulna, Bangladesh. November 19, 2005.