I am building a 16sq m wildlife pond in Wiltshire, England and someone who
is thinning out their pond in September has offered a whole range of plants
to get me started.
Unfortunately, their pond has azolla. Is this likely to be a problem?
There are some horrific photos on the web of large ponds and ditches
completely choked with azolla. But a garden pond owner who has azolla
states that their other plants keep it down to just a very small patch. I
imagine they compete for nutrients.
I don't expect any fertiliser runoff to enter the pond but I do expect to
top it up with tapwater. I suspect that azolla is only a problem when there
is excess nutrient in the water?

Anybody with experience?

thanks, Davy