The names ...salmi in Finnish and ...sundet in Swedish indicate that this missing feature should in fact be a strait (https://wiki.openstreetmap.org/wiki/Tag:natural%3Dstrait). If you choose MML Topographic map (MML stands for Maanmittauslaitos ie. National Land Survey of Finland) as the background layer in the OSM editors you'll find both names a bit southwest from this location.