Natural swimming pools - I want one

I'd like a natural swimming pool in my future eco-house. My dad has tried to transform a set of ponds into swimming poinds, up in Yorkshire, but it's very murky and there's only about 1 day each year when you might consider swimming in it... these ones look a lot nicer: http://www.theswimmingpondcompany.co.uk/about.html and a video: [youtube=http://www.youtube.com/watch?v=sTjHbXzvG6M&hl=en_US&fs=1&]