Maritime law is definitely not my forte, but I think the convention was related to the tolls imposed to pass through these waters (Sweden's Gota Kanal was built

Maritime law is definitely not my forte, but I think the convention was related to the tolls imposed to pass through these waters (Sweden's Gota Kanal was built to bypass this). It's also related to "innocent passage", which may not be so innocent in this case. Either way, there are probably provisions here for Denmark to close this off, as ultimately they are Danish waters.