sentences:  The plants also create a prime habitat for mosquitos, the classic vectors of disease, and a species of snail known to host a parasitic flatworm which causes schistosomiasis (snail fever).Directly blamed for starving subsistence farmers in Papua New Guinea, water hyacinth remains a major problem where effective control programs are not in place.Water hyacinth is often problematic in man-made ponds if uncontrolled, but can also provide a food source for goldfish, keep water clean and help to provide oxygen.