Small, free-floating stemless plants that thrive on the surface of still or slow-moving water, looking like a “carpeting” of tiny leaf clusters. Duckweed does not normally grow in rivers, they do tend to appear when there is reduced water flow. These plants are sometimes considered invasive species. If duckweed covers the entire surface of a pond, it will deplete oxygen, killing fishes while preventing other submerged plants from receiving sunlight necessary for them to grow. Duckweeds grow 20 times faster than a corn and is able to cover one acre in just 45 days, if unrestrained.