With regards to filtration, I suspect you will have to find that fine line for yourself. Somewhere between a muddy hole of water and an actual swimming pool is your answer. Skimmers in the aquarium world (especially salt water tanks) are incredibly beneficial when it comes to removing wastes where overcrowded conditions exist. If our wildlife population in the pond was kept low I don't think skimming would be all that important. I can't help but think that a large (grossly oversized for your pond volume) sand style filter system would be more beneficial, but be ready to replace the sand regularly.

When you joined PB and introduced us to swimming ponds, I thought to myself..."remotely clear water, merely most of the swimming season, will be the biggest challenge (besides snakes)." Without a large inflow of clear spring water there will be a considerable amount of money and time spent filtering, vacuuming and debris avoidance. With that said, your swimming hole could be between a quarter to a half million gallons. That is one large pool to filter and a pond is not near as forgiving as a traditional swimming pool.

UV filtration, in my very limited knowledge, is typically for bacteria control and I can only imagine the amounts of little microscopic critters you would be fighting off in a pond setting. Unless you are a germ-o-phobe, I personally would not worry about UV sterilizers.

I think that creating a pool-like concrete floor and walls would be the best money spent to help keep a swimming hole clean along with the proper vegetation surrounding the area to help filter all incoming water.

Disclaimer - I have no real experience in these matters, but I am enjoying the discussion and the challenges associated with your project.

Fish on!,
Noel