We have been considering such as well.
Now, very minimal info exists for creating a truly natural pond without electrical interference. I truly don't know why. I live in New England, surrounded by billions of old or current farms with a farm pond on it. Better believe none of them have electricity running to them and the only ones I see get truly scuzzy don't have natural pond plants in them, or get low and dry scuzzy without a water in source.
What I have managed to learn...
Whatever size pond you desire must mimic a natural ecosystem. This may take a bit of trial and error to get right and I'm no biologist so take this for what it's worth.
There are a variety of options to "seal" the bottom. Depending on what you choose (we may make use of an old pool liner) an amount of sand and stones sounds like the next best layer. Why? Natural filtration of sediment with a place for microbes to attach to and assist you with keeping water clean. Your ducks and local land (pollen,w tree debris, etc.)add plenty of sediment over time.
Give a good layer of rocks, gradually increasing in size, up the sloped (important for ducks and plants) sides. It's important to plant aquatic plants native to your region. Native, because pollinators and legality, plants themselves because they feed your ducks, allow hiding spots, and they filter your water while giving the microbes an important place to thrive.
All my research says that the microbes balance is crucial for your pond when going"natural". I think I said that already, sorry, sick as a dog.
I'll pop back in here in a bit.
