It sounds like this is your first pregnancy. Mine, too. I'm just over 20 weeks, and I wouldn't want to go. I've been paddling all summer with my doctor's blessing (until sitting in my ducky became painful), but her cutoff for big water is around 20-24 weeks. Aside from potential risks to the baby, you really have no idea how your body will respond to the different stages of pregnancy. Once the relaxin hormone kicks in, you may experience excruciating joint pain in your feet, SI joints of your hips, and various other places. You may not. There's no way to know. Right now, I cannot sit upright for more than 10 minutes at a time, and I feel as if my feet are being ripped apart. I'm still doing 4 HIIT circuits per week and prenatal yoga once or twice, but some days, I can't walk my dog. Additionally, there are some things that could pop up between now and your trip that require increased medical attention.
You could develop placenta Previa thatrequires bed rest, or all manner of other fairly common issues that pop up out of nowhere that can be life-threatening to you or your baby. If you are anything like me, you're annoyed and pissed about people telling you all the things you can't do, but I'm rapidly becoming more attached to a comfortable night's sleep and as many pain-free hours as I can muster in a day. That's just me, though. Also, keep in mind that your balance will get worse and risk of injury greater due to loosening ligaments and muscles as your pregnancy progresses. Ultimately, though, this a decision for you, your partner (making an assumption there), and to some extent, your doctor. Good luck, and I jealously wish you continued easy pregnancy.