The Copenhagen Convention,[1] which came into force on 14 March 1857,[2] is a maritime treaty governing transit passage through the Danish straits.
It has abolished the Sound Dues and all Danish straits have been made international waterways free to all commercial shipping.
[3] It had been increasingly evident that the Sound Dues had a negative impact on the port and merchants of Copenhagen, although the dues delivered by then one eighth of the Danish state income; and the world's seafaring nations were becoming less and less tolerant of these tolls and restrictions.
[5] A similar convention between Denmark and the United States, signed in Washington the same year, gave American ships free passage in perpetuity for a one-time fee of $393,000.
[5] A number of canals were built in part due to the trouble to pass the Danish straits.