My pair of ponds are fairly small, 5x9 with about 35' of stream and 9x12. Both are about 40" deep in places. I have lots of anacharis and several water lilies, along with a small bog. I've never cleaned the ponds, just add water to make up for evaporation and all the plants in the bog and along the stream. It stays crystal clear. There must be around 20 goldfish ranging from 3" to 9". There are also lots of native snails about 1" in size and I do mean lots!
In the 3 years and a couple months that it's been running, there must be about 1-2" of muck in the deep spots, although there is so much growth down there that it's hard to tell. Must must come from the fine volcanic soil here, which is super light and coats everything, inside and out. So whatever muck builds up is almost certainly from this. Yes, our house is dusty too, and I have to clean the computers at least every couple months, a cloud comes out.
Personally, I feel that unless the pond is way overstocked with fish and understocked with plant life, cleaning does more harm than good.
I also have a 55 gallon aquarium in the house with 2 6" or so goldfish (comet and shubunkin) and around 10 small bronze corydorus catfish. With lots of plants also, about all I do is feed them and change the filter once in a while if it clogs up. I haven't cleaned the aquarium, other than algae on the glass, in 3 years. Everything stays healthy, so why fiddle with what works! Oh, I do change about 1/3 of the water every month of so.