Wow, swimming in the mediteranian - cool! I have to agree with KSH about open water swimming. I can easily swim 750 in a pool but in open water, 500m is a struggle, you don't have to sight in a pool and that's when you lose your rhythm. I suggest you practice in open water a few times and don't forget, it you get tired you can do breathe stroke, back stroke etc. Yes, you can always stop and rest and remember - swim at the back of the pack, you will be less likely to get kicked, hit or swam over. No amount of pool swimming will prepare you for open water.

Please keep us posted on how you do and try to relax (I know, easier said than done) as you will save lots of energy that way!
Good luck and I admire your courage!!!!!!

tricat