Penny seemed to be interested in going for a walk on the smooth surface, so maybe it was lucky that this is an on-lead area. (But perhaps I underestimate her intelligence on that one. Maybe she just wanted a closer look.)
A list of water plants considered to be weeds in Victoria didn't include this one, so perhaps this growth isn't a big problem. Maybe when the seasons change it will disappear. I remember that when I had garden ponds - unfortunately, mostly removed because of the ongoing drought - I would get a growth of duckweed in certain seasons. However, I never had such a carpet as this one.
But it's certainly a beautiful sight.
I thought this was an interesting quote about duckweed:
The tiny duckweed plants grow fast in the cooler months when the water hyacinth slows down, helping to suppress mosquitoes and also purifying the water. It also provides lots of rich food for the compost. Duckweed is also regarded as a serious pest -- "a severe nuisance when present in large masses" -- as well as "the most promising plant for the twenty-first century". "Duckweed has potential for use in controlled ecological life support systems for human exploration and development of space." (NASA)