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