To check water pollution Eichhornia (water hyacinth) has been introduced in india. As this weed absorbs mercury, cadmium, lead and nickel from sewage water. It is considered as worlds most problematic weed as it is on invasive species. If water hyacinth is not controlled, it can covers the enitre pond or lake and whole water flow. It blocks sunlight also, acts as prime habitat for mosquito (vector snails host for flatworm and starves water of oxygen.