Beavers may be nature’s chief engineers when it comes to enhancing biodiversity but holes in the river dykes are among the less appreciated results of their activities, water authorities in the province of Gelderland have said.

Beavers (Castor fiber) were hunted for their fur and musk and became extinct in the Netherlands in the early 19th century. Since their re-introduction in the 1990s, however, the population has gone up to 5,000 nationwide.

Some 1,500 live in Gelderland which is home to the country’s big rivers Waal, lower Rhine and Meuse. Their number is set to double every four years and that is causing problems,  local water authority Henne Ticheler told local broadcaster Gelderland.

‘Beavers like to dig and that weakens the dykes and they also burrow into the paths used to monitor waterways. That means tractors or cranes can come a cropper because of holes,’ Ticheler said. Dams built by the beavers can also impede drainage and increase water levels which affects agriculture, he said.

Gelderland has started so-called beaver patrols at night to chase the animals away. The dykes are also fitted with wiring to discourage burrowing beavers.

In 2020 the water authorities in Gelderland spent €25,000 to repair and prevent damage done by beavers. That will increase as beaver numbers grow, official said.

So far the province has not said it will actively cull beavers.