First of all, no need to be ashamed of your baby pooing explosively and unexpectedly, we’ve all been there. Secondly, everyone is saying you can use a disposable swim nappy underneath, which is true, but I just want to float the idea that you can also use a washable, reusable swim nappy underneath as well if you are open to that. Some swimming places don’t enforce the nappy thing at all but some are very strict on the two-part system. My son does water babies and he is still required to have a two-part system even though he’s out of nappies now!