Never let anyone talk you into putting duckweed, or any other floating weed, into a pond. Duckweed (Lemna sp.) spreads very quickly in still or slow moving, nutrient-rich water. It grows 30% faster than water hyacinth and can actually double in size in a few days. Duckweed is difficult to eradicate and it grows back rapidly, often from hidden pieces of frond or dormant submerged seed.
Floating pond weed:
may indicate that you are over feeding your fish
chokes the surface of the pond and cuts off gaseous exchange
can be transported to nearby rivers or creeks by animals and waterbirds
Duckweed alternatives:
Alternatives to duckweed include waterlilies and nardoo. Nardoo (Marsilea drummondii) is an Australian fern species that has clusters of fronds growing from long, creeping rhizomes. The fan-shaped leaflets float on the surface of the water.
