neo, no doubt it could be done. As Bobad said, making it a lined pond would certainly be easier to keep pristine. Keeping organic debris from entering would be needed
With a lined pond, you will essentially have a very basic swimming pool since you wouldn't have the soil problems. Put in a big grass buffer in the inflow and keep the soil open with aerator spikes occasionally. Add a bog area to take up nutrients (i'd keep a few fish there to eat insect larvae), and about 4000 watts worth of UV with pump intakes in several areas and you might knock the filter maintenance down to 1-2 hours per day. Add a chlorine injector and you could knock it down to 1-2 hours per week, but then you're back to a swimming pool.
What is your goal that requires such clear, filtered, and sterile water?
