Don’t want to be a fish
Just a cheap and quick test. Got a cheap lavalier mic, put some cling film on it and attached it to a mono pod. Then put it all into the canal while one of the tour boats passed.
If I do it again I need to find a better way to make sure that my handling of the mono pod can’t be heard. Also the phone don’t cut of the inboard mic so you can still hear what is going on above water.