The unique landscape of the ‘Wijers' owes its special location to the transition between the Kempen plateau and Haspengouw. With its permeable sandy soil, the Kempen plateau forms the infiltration and source area of the ‘Wijers'. This is where the parallel stream valleys originate, that flow south-westward and structure the area of the ‘Wijers'. The infiltrated water seeps through to the subsoil in many places in 'De Wijers'. Which is instantly the ideal foundation for the construction of the typical ponds in the region.
Not all ponds originated at the same time or have the same origin. The oldest fish ponds date from the 13th century and are located in De Maten in Genk. The fish ponds in the Dauteweyers nature reserve in Diepenbeek were only created in the 18th century and were first used for mining iron ore. The ponds on the Terlaemen Estate in Heusden-Zolder were first used as fishing ponds in 1880. Before that, they were used to extract peat. The huge explosion of the number of ponds occurred in the 19th and 20th centuries, under the influence of the Zonhoven fish farmers, who made farming an economic activity.
The ponds of the ‘Wijers' are man-made. Until the beginning of the 20th century, they were created by mending fens or by damming lower areas. After WW II, hayland was dug up into a cluster of ponds. The ponds were mainly used for the breeding of carp - an important part of fish farming in Zonhoven to this day.
The ponds were constructed in the stream valleys according to an ingenious dike system. Incoming water was held up by a dike, creating a deeper pond suitable for fish farming. The water level was maintained by inlets and outlets. Downstream, the next fen was dammed, creating a string of ponds.
Later, ponds were created with dikes on all four sides to grow more fish. One pond ran into the next and over time, a pond system was created.
Abbey of Herkenrode
An important period for the 'Wijers’ was the late Middle Ages (12th and 13th centuries). In the 13th century, the first ponds were created by peat and iron mining. The Kempen soil contained high volumes of peat. Under the influence of the monasteries (especially the Abbey of Herkenrode), these pits were later used for fish farming. The Abbey of Herkenrode (Cistercian nuns) also managed the Bokrijk Estate.
The promotion of fish farming by these monasteries had several reasons:
- In the Middle Ages, Catholics were not allowed to eat meat originating from 'four-legged animals' on Fridays. During Lent, no meat was allowed either. Fish offered a viable alternative and was, as such, an important source of food.
- Another reason why the monasteries and convents massively encouraged fish farming was that they hoped that the population would have more time to pray if they ate a lot of protein-rich fish.
- Finally, freshwater fish from fish farming ponds were a cheaper and fresher alternative to sea fish.
- Fish farming was simply more lucrative than agriculture.
Over the centuries, the ponds were expanded into a complex of hundreds of connected ponds. The Zonhoven fish farms are still the best proof of this. To supply the ponds with water, several locks were installed at a later date. The ponds are interconnected according to the principle of connecting vessels. Every year in the autumn, a number of ponds are drained to make it easier to catch the farmed fish.