User blog comment:Blackendedsoul/DF Swimming./@comment-3130944-20110309175245/@comment-3326484-20110309233918

I am pretty sure that they were both wearing intertubes in that scene. Oda may have decided that df users can be in water if they are using something to float in it. Also, this question may have already been asked. read up on some of the SBS to see if they have an answer there.