Oh, this is the story of my life! If you do lap swimming, consider a cap. (Yeah, I know they look stupid.) Take it from someone who swam competitively for 11 years
that it makes a world of difference. I recommend one made of silicone rather than latex. They cost about 5x more, but are infinitely more comfortable and last forever. Before you put it on, wet your hair with fresh water in the shower and work conditioner through it. This prevents your hair from absorbing much chlorine at all.
Obviously, this won't work for a lifeguard (something I did as well!). Assuming your hair is somewhere near or past your shoulders, this will work. After you wash your hair, squeeze out all the water you can and put on conditioner, but don't rinse it out. Comb it back like a ponytail and twist into a bun-ish shape. Don't put an elastic around it, though, because after a few days your hair will start to break. Instead, get a bunch of little clips and put them around the outer edge of the coil until it stays up. While you sit in the sun, it heats up and soaks into your hair-a deep treatment every day! My hair was always in better shape AFTER the summer because of this little trick.
Also, the shampoo I swear by is Malibu "C" Swim&Sport. Kinda hard to find sometimes (I get mine at a sporting goods store that deals with swim teams, but some salons carry it as well), but worth the search. If you can't find that, Ultra Swim from the drugstore is good too (but smells funny...). Hope this helps.