I would guess the swimming area would be a concrete inground pool with the top rim lowered a few feet below grade. Then a much larger area would be 2-3 foot deep wetland full of plants, gravel, and sand through which water is circulated. There is likely some magic ratio between the two areas that works well.
UV is pointless. Losing battle there, and you would be destroying the very life you are emplying to clean the water.
Personlly I would want some non reproducing fish in the pond to keep the numbers low, but get after bug larva. Not sure what that would be. First thought would be mollys each spring. They would be killed in cold water, but would do thier jobs during the bug season.