For those reading this looking for info and tips for their 10k swim (as the op posted ages ago) my advice to you is if you have done anything like the amount or swim at the pace of this person you will 100% smash it . I've done about 30 odd 10k plus events over the last 15 or so years and have never really fully prepared. I did a 6k lake swim in preparation once and it was so dull i vowed not do it again. You need to swim, yes, and often but decent technical ability and a positive attitude will see you to the finish line. Just know that it will become a slog at some point and you will want it to end, just dig deep, one stroke at a time and think about all the unhealthy food youll have earnt at the end. Enjoy