Dhaka, Jan. 11 -- Through the labyrinthine waterways of the Sundarbans -- the world's largest mangrove forest and a UNESCO World Heritage site -- luxury cruise vessels glide like steel leviathans, their engines growling through the quiet, diesel fumes trailing behind them like smoke from a warship.

Even at anchor, the generators hum incessantly, keeping air-conditioning and swimming pools alive while the forest's nocturnal symphony -- birdsong, rippling water, the rustle of leaves -- is drowned out by artificial lights, booming music, and the roar of engines.

Tourists peer from glassed-in rooms at the sprawling mangroves, the bright winter sun filtered through tinted panes, oblivious to the subtle poisoning of the waters beneath them. ...