I agree with RAH. I don't think you can turn a pond into a "swimming pool" without some kind of system to control algae.

City pools use lots of chlorine. I think the best pond option is to use plants to take up the nutrients, and essentially starve the algae.

Here is a link that gives more background on the theory of natural "swimming pools".

Natural Swimming Pools

I also agree with Theo, that some fish will make your pond better. If legal in Texas, I would definitely consider stocking gambusia (mosquito fish).