Split not quite in half by the border between India to the west and Bangladesh to the east, crowning the Bay of Bengal, the world’s most complex river delta works like South Asia’s showerhead—one the size of Lebanon or Connecticut. Fed by Himalayan snowmelt and monsoon runoff, carrying a billion tons a year of Asian landmass suspended as sediment, the three great flows of the Ganges, the Brahmaputra and the Meghna rivers all end in one vast estuarial tangle, one of Earth’s great water filters, the mangrove forests of the Sundarbans.In seasonal rhythm with the monsoon, more than 450 curling rivers and creeks make up this vast showerhead’s nozzles, running full in the hot, rainy summer and sluggish in the warm, dry winter. Some waterways clog with sediment for years, or forever; new ones form. Others get dammed or channeled by shrimp and rice farmers. As disruptive as these can be to a hydrological dance that balances the freshwater flows with the salty tides that drift tens of kilometers inland, they are nothing so dramatic as the occasional cyclone that pushes the sea itself far back up the showerhead.