Here is an excellent video featuring the former Japan synchronized swimming team in various hot springs (onsen) around Oita Prefecture. I have been to some of these myself, and can attest to the magic of both the location and the waters. However, I hate to pee in the pool here, but there are several things happening here that are absolutely impermissible by Japanese standards (in fact, they were cited as reasons for excluding all “foreigners” entry to the baths during the Otaru Onsens etc. Case of 1993-2005):

Making noise in the bathing area.
Splashing about.
Wearing bathing suits in the pool.
Wearing towels in the pool.
Mixed bathing in a non-rotenburo area.
Not washing off one’s body completely before entering (note that they get in dry after only a cursory splash).

If anyone does any of these things in real life, they will probably get thrown out of the bathhouse. Worse yet, if anyone who DOESN’T LOOK JAPANESE did anything like this, everyone who doesn’t look Japanese (i.e., a “foreigner”) a priori would be denied entry at the door, merely by dint by phenotypical association. That’s why I have a hard time enjoying this video knowing the history of Japanese public bathing issues, where stone-headed onsen owners looked for any reason to enforce their bigotry on people they thought couldn’t learn Japanese bathhouse rules. Instead, without any irony whatsoever, we have the Japan synchro swim team breaking most of them. To raucous applause. Good thing they didn’t bring in a NJ synchro team to do this stunt — because then “cultural insensitivity” would creep into the mix.