Invasive rodent threatens Danish flood defences as experts warn of spreading infestation

A large, invasive South American rodent capable of undermining dikes and flood defences has been shot in southern Denmark, with experts warning the species is likely spreading into the country, Danish broadcaster DR reports.

A hunter killed a coypu—also known as a nutria—weighing 11 kilograms and measuring one metre in length near Skærbæk in late April, according to Tønder Municipality. The semi-aquatic rodent, native to South America, burrows into embankments along waterways, weakening their structure and increasing flood risks, said Morten Elmeros, a senior advisor at Aarhus University’s EcoScience department.

“It digs into the banks, and if those banks are part of dikes or levees, there’s a risk of flooding—or that the dikes become weaker during floods, making them easier to breach,” Elmeros told DR.

Local regulatory hunter Kjeld Lautrup shot the animal near a large lake where he maintains a feeding station equipped with a wildlife camera, originally set up to monitor invasive raccoon dogs. “We try, of course,” Lautrup said. “We roughly know the area they inhabit, and as soon as we get reports of coypus, we attempt to shoot them.” Yet he acknowledged the difficulty: Denmark records only two or three kills annually, making detection unlikely.

Lautrup warned of the rodent’s destructive potential, citing severe infestations in Germany and the Netherlands, where authorities employ full-time staff to combat the species year-round due to its damage to dikes and dams.

Elmeros confirmed the coypu has appeared sporadically in Denmark for years, often escaping from private collections or zoos, but recent climate-driven milder winters and its northward expansion through Germany suggest a growing permanent presence. “There’s likely an immigration into Denmark underway,” he said.

Beyond threatening flood defences, the rodent also damages crops and native vegetation. Elmeros stressed the need for culling but cautioned against misidentification: “You have to be careful before shooting at something brown in the water—it could be an otter, which is similar in size.”

Coypus typically measure 40–60 centimetres in body length, weigh 5–10 kilograms, and have brown or yellowish fur with distinctive orange incisors.