I marked them as private to be consistent with the tagging of, for example: 
- https://www.openstreetmap.org/way/93079001
- https://www.openstreetmap.org/way/38114519
- https://www.openstreetmap.org/way/93079001
Those facilities are not supposed to be accessed from outside the beach, as far as I know : 
https://www.stadt-zuerich.ch/de/stadtleben/sport-und-erholung/sport-und-badeanlagen/sommerbaeder/mythenquai.html 
 