The North Sea is semi-enclosed and shallow, except for the northernmost part. Its ecosystem is becoming increasingly fragile owing to the intensity of human activity, on and off-shore.
Since the 1970s, the North Sea has been Europe's main offshore-oil-extraction site. The EU’s three biggest ports – Rotterdam, Antwerp and Hamburg – are situated on the North Sea coast. The region is also home to most of the world's maritime organisations and service providers. There is still an active fisheries industry. Though fishing itself is in decline, fish and seafood are still traded and processed in a great many places. Aquaculture is now established too, with various species farmed – mussels in the south and salmon in the north, for example.