Regarding https://www.openstreetmap.org/node/2125473109

Where did the use of waterway=access_point come from? 

I do not find it on the waterway page, nor anywhere else after a few quick searches of the wiki.
https://wiki.openstreetmap.org/wiki/Key:waterway

That location is a canoe=put_in;egress
I see now that back when I updated its tags I had forgot to add "egress". Still, it shows up well enough on OpenStreetBrowser.
https://openstreetbrowser.org/#map=17/44.65966/-84.71000&basemap=osm-mapnik&categories=paddling_hazards,paddling_routes,paddling_amenities

See the Michigan Wiki page:
https://wiki.openstreetmap.org/wiki/Michigan#Water