A two-year study for the Kerala State Biodiversity Board finds the water lily, which appeared in Malarikkal after the 2018 floods, has shown unprecedented and uncontrolled growth; ecologists flag its impact on local aquatic plants, water flow and sunlight penetration, besides concerns over methane emissions from decaying plant biomass; the seasonal bloom has transformed Malarikkal into a tourism hotspot, bringing additional income to farmers, boat operators and local residents