not sure that water taxi fit the schema for taxi stands: https://wiki.openstreetmap.org/wiki/Tag:amenity=taxi?uselang=en seems like thats only for land based taxis. If thats the case then suggest retagging all pois in this area that are water taxis as perhaps ticket office or office or something else... example of poi: https://www.openstreetmap.org/way/211888935