Duckweed (lemna minor) is a small plant that grows on the surface of the water. Each floating leaf on the plant is attached to a single, tiny root that extends into the water. Duckweed grows best in slow-moving water like the water in a pond or a bayou. Duckweed grows all over North America, but it grows best in warm, sunny locations. Because it grows on the surface of the water, overgrowth of duckweed in some areas can reduce oxygen exchange and cause low oxygen levels in water.