This should not be simply mapped as highwy=path.  Although the entrance on the south (Burgos) side is not physically blocked, the tunnel is unlit and submerged in water.  Passing through it would be an adventurous, wet, and dark expedition, if not physically blocked somewhere away from the south entrance.  With highway=path, routing engines will route people through it and this shouldn't be.  I'm not sure what the correct way to tag it would be, but maybe someone with deeper knowledge of OSM can come up with something appropriate.