In modern times, artificial seabed channels have been dug, many reefs have been dredged either by sand pumping or boulder clearance,[1] and a well-developed light signaling network has been installed to protect the heavy international traffic on this small sea.

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

On the South: The limits of the Baltic Sea in the Belts and Sound: According to Den Store Danske Encyklopædi and Nudansk Ordbog [da], the name is from the Dutch words katte 'cat's' and gat 'gate, passage'.

It derives from late medieval navigation jargon, in which captains of the Hanseatic trading fleets would compare the Danish straits to a passage so tight that even a cat would have difficulty squeezing its way through, owing to the many reefs and shoals.

[9] Beginning in 1429 in the Middle Ages, the Danish royal family – and later the state of Denmark – prospered greatly from the Sound dues, a toll charged for passage through the Øresund, while Copenhagen sheltered and repaired ships and provided trade opportunities and protection from piracy.

Unlike those in most other places (including the North Sea and Skagerrak), the Kattegat's cold seeps are at relatively shallow depths, generally from 0 to 30 m (0–100 ft) below the surface.

[12][13] Due to their distinct properties, the Kattegat bubbling reefs are under protection and are recognised by the European Union (EU) as a Natura 2000 habitat (type 1180).

[14] The Kattegat, characterised by widespread anoxia,[15] was one of the first marine dead zones to be noted in the 1970s, when scientists began to study the effects of heavy industry on the natural world.

The remaining larger shallow reefs are among the protections, as they are important spawning and feeding grounds for fish and marine mammals and support a thriving but threatened biodiversity.