Lennik (Brussels Morning Newspaper) – Rangers at Groenenberg Castle, Lennik, led by Tom Brichau, are removing invasive carp from the pond to protect toads, frogs, dragonflies, waterfowl, and bats, with similar work planned at Krommeviver, Gaasbeek Castle.
As VRT News reported, rangers at Groenenberg Castle in Lennik, in the province of Flemish Brabant, Belgium, are removing a large number of invasive carp from the castle pond today, Oct 30, 2025. They mentioned that the fish have grown in huge numbers over the years. They are taking up most of the food in the pond. Other animals that live in or near the water are now staying away.
The lack of food is upsetting the natural balance of the pond. To remove the carp, experts are using a method called electrofishing. A safe electric current is sent through the water. This stuns the fish and makes them float to the surface. Rangers then collect the fish with nets.
What is being done to remove invasive carp at Groenenberg pond in Lennik?
Once caught, the carp are placed in large water-filled containers for transport. They are released into other waterways, including the Dender River and the Brussels-Charleroi Canal. Some of the carp will also go to the ponds at Coloma Castle in Sint-Pieters-Leeuw. There, they will support local carp fishing.
“That’s good news for fishing enthusiasts, because after today, the stock will be well replenished,”
says ranger Tom Brichau.
“So far, we’ve mainly caught a lot of carp.”
According to officials, the main goal is to create better conditions for amphibians and insects. Toads and frogs will benefit directly. Dragonflies and other water insects will have more space and food. Waterfowl that feed near the pond will also benefit. Bats will gain because they feed on the insects that live around the pond.
“They’ll now be able to find and catch many more insects. This way, the pond will recover ecologically.”
The pond is completely emptied during the work. Removing this material prevents nutrient overload and helps restore the pond’s ecosystem. Rangers have used this method before. A similar operation is planned soon at the Krommeviver pond at Gaasbeek Castle to continue protecting local wildlife.
“We’ve already done this in one of the ponds at Gaasbeek Castle, right here,”
explains Brichau.
“It turned out to be very effective.”
The pond at Groenenberg Castle in Lennik was constructed in the late 1700s along with the castle’s landscaped gardens. Recently, ecologists have noticed a remarkable rise in non-native carp, which has occupied the pond and is feeding off the food naturally for wildlife. During the summer of 2024, the conservation authorities announced plans to drain and remove the invasive fish, as well as the organic material that had accumulated in and around the pond. Work is now being undertaken as of October 2025.
