The western shore of Jutland may qualify as the North Sea but the other two regions definitely don't. Morever, the top layer of the Kattegatt has a much lower

The western shore of Jutland may qualify as the North Sea but the other two regions definitely don't. Morever, the top layer of the Kattegatt has a much lower salinity compared to the ocean due to significant outflow of warm brackish water from the Baltic, carrying all the pollutants to the North Sea through the Skagerrak. To be fair, the situation has actually been improving since the late 90s with tighter regulation on effluents, however I'd rather wait another 10 year before this patch of sea clears up itself.