I’ve never owned a pond that hasn’t suffered with duckweed – quite a pretty weed, as weeds go, but nonetheless a weed. It is utterly prolific: I fished out every last dot a week ago, until we had clear water, and just look at it again.
The trouble is they get caught in just about everything, from waterlilies to bits of liner, and so there’s no way you can hope to get them all out. Just one or two left in a little cranny somewhere, and you’re condemned to another fishing expedition a week later.
The silver lining is that because it virtually covers the water’s surface in our rather under-planted little pond, we never have problems with green water or algae as it simply out-competes it. I still wish we had more plants and less duckweed though…