The correct option is C Oxygen
Eichhornia crassipes, commonly known as common water hyacinth, is an aquatic plant native to the Amazon basin and is often a highly problematic invasive species outside its native range. When not controlled, water hyacinth will cover lakes and ponds entirely which affects water flow and blocks sunlight from reaching native aquatic plants which often die. The decay processes deplete dissolved oxygen in the water, often killing fish (or turtles).