A wattle fence arranged at an acute angle in a zigzag pattern at the mouth of a river, in which the fish become entangled by the current: Since the Middle Stone Age, coastal dwellers in Europe have caught fish in this way, in the Wadden Sea as late as the 20th century.
The oldest still functioning fish fence is in Kappeln in the Schleswig-Flensburg district in the Schlei. The herring fence has been mentioned in documents since 1451 and is the last of what used to be around 38 installations of this kind in the estuary of the river.

To preserve this historical heritage, the inhabitants of the town have been celebrating the Kappeln Herring Days since 1978.
Every year on Ascension Day, the Schleistadt is in a state of emergency for four days: around 80 showmen and market traders present their offerings directly on the harbour mile.
Rides, herring stands and music stages  - from rock to shanty to children's disco - create a festive atmosphere.

Ships cruise on the Schlei and in the Baltic Sea, taking visitors on a trip. In the locomotive trekking at the southern harbour, different teams have to pull an old diesel locomotive with a rope over a distance of about 50 metres. The highlight, however, is the celebrity bet in which well-known personalities of the country estimate the weight of the herring catch. The winner gets to wear the crown of herring king.