Duckweed (Lemna minor), or water lentils, choking a waterway in Ohio. These free-floating plants will appear in mid-summer and then vanish by fall. The plants provides habitat for many small aquatic species including bacteria, protozoa, fungi and other micro-invertebrates. Sometimes, though, they can become a nuisance by taking over quiet waterways and ponds, and depleting oxygen that is vital to many organisms as well as restricting sunlight to other aquatic plants. Duckweed is a high-protein food source for waterfowl and is also eaten by humans in some parts of southeast Asia.