Duckweed (Lemna Minor) is an tiny invasive floating plant which can replicate very rapidly. These small plants can cover an entire pond or lake surface very quickly if left unchecked. Duckweed is usually a sign of excess nutrients in the pond. The carpet of duck weed can block sunlight and affect fish and submersed pond life. Duckweed can be skimmed from the water surface using an algae net and specific water treatments can be used to disrupt the plant growth.