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Kattegat and Skagerrak

The Kattegat (Danish: [ˈkʰad̥əɡ̊ad̥]) or Kattegatt (Swedish: [ˈkatːəˈɡatː]) is a 30,000 km2 sea area bounded by the Jutlandic peninsula in the west, the Danish straits islands of Denmark to the south and the provinces of Västergötland, Scania, Halland and Bohuslän in Sweden in the east. The Baltic Sea drains into the Kattegat through the Danish Straits. The sea area is a continuation of the Skagerrak and may be seen as a bay of the Baltic Sea or the North Sea or, as in traditional Scandinavian usage, neither of these.

The Kattegat is a rather shallow sea and can be very difficult and dangerous to navigate, due to the many sandy and stony reefs and tricky currents that often shift. In modern times, artificial channels have been dug, many reefs have been dredged by either sand pumping or stone fishing, and a well-developed light signaling network has been installed, to safeguard the very heavy international traffic of this small sea.

There are several large cities and major ports in the Kattegat, including Aarhus, Gothenburg, Aalborg, Halmstad and Frederikshavn, mentioned by descending size and importance.


Älvsborg at Gothenburg, a sea fortress in the Kattegat

According to the definition established in a 1932 convention signed by Denmark, Norway and Sweden (registered in the League of Nations Treaty Series 1933–1934), the northern boundary between the Kattegat and Skagerrak is found at the northernmost point of Skagen on Jutland, while the southern boundary towards Øresund is found at the tip of Kullen Peninsula in Scania.[1]

Waterways that drain into the Kattegat are the rivers of Göta älv at Gothenburg, together with the Lagan, Nissan, Ätran and Viskan in the province of Halland on the Swedish side, and the river of Gudenå in Jutland, in Denmark.

The main islands of the Kattegat are Samsø, Læsø and Anholt; the latter two, due to their dry summer climate, are referred to as the Danish desert belt.

A number of noteworthy coastal areas abut the Kattegat, including the Kullaberg Nature Reserve in Scania, Sweden, which contains a number of rare species and a scenic rocky shore, the town of Mölle, which has a picturesque harbour and views into the Kullaberg, and Skagen at the northern tip of Denmark.

Currently, a proposal for a bridge from Jutland to Zealand across the southern part of the Kattegat is under political consideration in Denmark. It would link the islands of Zealand and Samsø with continental Denmark.


The International Hydrographic Organization defines the limits of the "Kattegat, Sound and Belts" (that is, the Kattegat, Øresund, Great Belt, and Little Belt) as follows:[2]

On the North: A line joining Skagen (The Skaw, northernmost point of Denmark) and Paternoster Skær (57°54′N 11°27′E / 57.900°N 11.450°E / 57.900; 11.450) and thence northeastward through the shoals to Tjörn Island.
On the South: The limits of the Baltic Sea in the Belts and Sound:


According to Den Store Danske Encyklopædi and Nudansk Ordbog, the name derives from the Dutch words kat (cat) and gat (hole, gate). It derives from late medieval navigation jargon, in which captains of the Hanseatic trading fleets would compare the Danish Straits to a hole so narrow that even a cat would have difficulty squeezing its way through, on account of the many reefs and shallow waters.[3][4] At one point, the passable waters were a mere 3.84 kilometers (2.39 mi) wide. The name of the Copenhagen street Kattesundet has a comparable etymological meaning, namely "narrow passage".[4]

An archaic name for both the Skagerrak and Kattegat was the Norwegian Sea or Jutland Sea (Knýtlinga saga mentions the name Jótlandshaf). Its ancient Latin name was Sinus Codanus.[5]


Control of the Kattegat, and access to it, have been important throughout the history of international seafaring. Until the completion of the Eider Canal in 1784, the Kattegat was the only water route into and out of the Baltic region.

Since 1429 in the Middle Ages, the Danish royal family – and later the state of Denmark – has prospered greatly from the Sound dues (toll) charged for passage through the Øresund, while Copenhagen provided shelter, trade and repair opportunities and protection from piracy. The dues was eventually lifted in 1857.


In the Kattegat, the salinity has a pronounced two-layer structure. The upper layer has a salinity between 18‰ and 26‰ and the lower layer - separated by a strong halocline at around 15 meters -, has a salinity between 32-34‰. The lower layer consists of inflowing seawater from the Skagerrak, with a salinity on level with most other coastal seawaters, while the upper layes consists of inflowing seawater from the Baltic Sea and has a much lower salinity, comparable to brackish water, but still a great deal higher than the rest of the Baltic sea. These two opposing flows transports a net surplus of 475 km3 seawater from the Baltic to the Skagerrak every year.[6] During stronger winds, the layers in the Kattegat are completely mixed in some places, such as the Great Belt, so the overall salinity is very variable in this small sea. This sets some unique conditions for the sealife here.[7]

Ecological collapse[edit]

The Kattegat was one of the first marine dead zones to be noted in the 1970s, when scientists began studying how intensive industrial activities affected the natural world.[8][9] In recent years studies and research, for instance, have given much insight into processes like eutrophication, and how to deal with it. Denmark and the EU have initiated costly and far-reaching domestic projects in order to repair, stop and prevent these environmentally destructive and economically damaging processes,[10] since the first Action Plan for the Aquatic Environment in 1985, and are now busy implementing the fourth Action Plan. The action plans sum up a broad range of initiatives and include the so-called Nitrate Directives.[11] The action plans have been viewed as a success, although the work is not finished and all goals are not completely met yet.[12]

Protections and regulation[edit]

Grenen in Denmark is important for bird migrations and is a protected area.
Bjärekusten Nature Reserve with Hovs Hallar in Sweden.

Due to the very heavy sea traffic and many large coastal settlements, Kattegat has been designated as a Sulphur Emission Control Area as part of the Baltic Sea, since 2006. The benchmark for sulphor in fuels was recently lowered to 0.1%, to be effectuated from 1. January 2015.[13]

Several larger areas of the Kattegat are designated as Natura 2000 and under various bird protections such as the Ramsar Convention. The remaining larger shallow reefs, are among the protections, as they are important spawning and feeding grounds for fish and marine mammals and they supports a thriving but threatened biodiversity. Protected areas includes:


See also[edit]



  1. ^ Convention No 3210. League of Nations Treaty Series 139, 1933–1934. Retrieved 27 December 2012.
  2. ^ "Limits of Oceans and Seas" (PDF) (3rd ed.). International Hydrographic Organization. 1953. Retrieved 6 February 2010. 
  3. ^ Den Store Danske Encyklopædi (2004), CD-ROM edition, Copenhagen: Gyldendal, entry Kattegat.
  4. ^ a b Nudansk Ordbog (1993), 15th edition, 2nd reprint, Copenhagen: Politikens Forlag, entry Kattegat.
  5. ^ Wikisource-logo.svg Gilman, D. C.; Thurston, H. T.; Colby, F. M., eds. (1905). "Cattegat, The". New International Encyclopedia (1st ed.). New York: Dodd, Mead. 
  6. ^ Ærtebjerg, G., Andersen, J.H. and Schou Hansen (2003). "Hydrography". Nutrients and Eutrophication in Danish Seawaters. Danish Environmental Protection Agency and National Environmental Research Institute. Retrieved 30 January 2016. 
  7. ^ Matti Leppäranta nad Kai Myrberg (2009). Physical Oceanography of the Baltic Sea. Springer-Praxis. p. 72-74. Retrieved 30 January 2016. 
  8. ^ "Further Rise in Number of Marine ‘Dead Zones’". UNEP. 19 October 2006. Retrieved 30 January 2016. 
  9. ^ Karleskint, Turner and Small (2013). Introduction to Marine Biology (4 ed.). Brooks/Cole. p. 4. Retrieved 30 January 2016. 
  10. ^ Both the ecosystems and the Danish fishing industry has suffered greatly from the eutrophication of the Kattegat sea. (Source: Bo Barker Jørgensen and Katherine Richardson: Eutrophication in Coastal Marine Ecosystems Coastal and Estuarine Studies, American Geophysical Union 1996, ISBN 0875902669, Ch. 8)
  11. ^ Implementation of the Nitrates directive in Denmark Danish Ministry of the Environment
  12. ^ Jesper H. Andersen and Jacob Carstensen (25 October 2011). "Action Plans for the Aquatic Environment have been a success". Politiken (in Danish). Retrieved 24 November 2014. 
  13. ^ "New sulphur regulations may lead to distortion of competition in the shipping industry". MT Online. 12 August 2014. Retrieved 19 January 2016. 
  14. ^ "Natura 2000" (in Danish). Danish Nature Agency. Retrieved 19 January 2016. 
  15. ^ "Natura 2000" (in Swedish). Swedish Environmetnal Protection Agency. Retrieved 19 January 2016. 

External links[edit]

Media related to Kattegat at Wikimedia Commons

Coordinates: 56°55′42″N 11°25′41″E / 56.92833°N 11.42806°E / 56.92833; 11.42806