Just about the time the duckweed finally starts to die off, the trees over the pond start dropping their leaves and every day I'm trying to keep them sieved out of the water. Fortunately they don't have too many leaves left now.
I used to have a (neighbours) Holm Oak near my pond, (it's been chopped down for a while now cos it went berserk and got huge after a good trim one year): just as the garden is getting tidy in late spring the damn thing drops all it's old leaves - it's like have Autumn all over again.
The trouble is that one side of it is up next to the fence, and it's impossible to get around that side because of the three fruit trees growing there, (unless I want to end up having a bath with the frogs!)
I've got a sieve attached to a long bamboo cane and I fish the leaves out every day or so with that... it's not too irksome a chore. I even enjoy it some days- gives me an excuse to potter around out in the garden in the morning.