I believe the issue with timbers and swimming pools is more their interaction with moisture than with chlorine. The combination of poor humidity control with a species of wood that has poor rot resistance can be a disaster. -- structural failure in a few years. Thus, I have always felt that, with the exception of a few special species (like teak and cypress), timbers and pools don't mix.
On the other hand, I've seen examples of pool enclosures that have been claimed to perform very well. At our recent Western Conference, Bill Keir (moderator of the UK forum below) showed us photos of a beautiful pool building framed in English Oak that has had no problems whatsoever. Most framers who do high-end residential work have done a pool enclosure or two and could probably comment from direct experience.
[This message has been edited by Brian W (edited 04-15-99).]