There often are places people use for swimming, that are not beaches. Usually it's just some grassy area by a lake or river, most often - unofficial. This is being requested more and more often, and in many cases those are mapped as beaches - but that seems to be incorrect. https://help.openstreetmap.org/questions/6337/icon-for-beaches-or-access-to-the-water asked for an icon for this, but not about tagging. Another related request was about mapping unofficial mooring places: https://help.openstreetmap.org/questions/26237/unofficial-mooring-place-how-to-map-it . asked 23 Oct '17, 06:40  Richlv |
One Answer:
You can tag with answered 24 Oct '17, 06:59  aharvey |
While it does sound wrong (it's not much of a "sport"), we have lots of such cases (like highway=path). Somewhat surprisingly, https://wiki.openstreetmap.org/wiki/Swimming_and_bathing#Natural_water_where_swimming_is_possible even recommends that - will go with it then, thank you.
Based on tag usage, "leisure=swimming_area" is also commonly used to mark outdoor water areas used for swimming. See https://wiki.openstreetmap.org/wiki/Tag:leisure%3Dswimming_area .