Unless your child has immune issues I probably wouldn't be too concerned. That said, it would be really easy to put a large tegaderm type dressing over the site for the short while you'd be in the water with the dolphins. I know that for some reason my daughter's site is irritated by ocean water, so I just put a large tegaderm over it the once a year we go to the beach (well, two, one over the G and one over the J!). If you do this, wipe the area down with some alcohol or skin prep pads where the tape will go, so it will adhere better to the skin (and watch any sunscreen you use, avoid it around that area), a leaky dressing will just hold the same water close to the skin, potentially worse than free flowing water around it.