Norfish Danish Limfjord Herring Fishery 1518-1835

Until a breach at Agger Tange in 1825, affording access to the North Sea, the only access was to the east via the Kattegat. The breach enabled salt water to penetrate the Limfjord which had previously been brackish.

It may be argued that despite the obvious, radical changes to the salinity, hydrography and nutrient levels that the breach caused, herring fishing was impacted prior to this event by a combination of fishing methods and the destruction of spawning grounds.