During the week, a resident of Luxembourg-ville was walkig through the Pétrusse valley whe she spotted what turned out to be a copyu, a large rodent which can cause devestation to local environmental habitats by overgrazing.

The first copyus in Luxembourg were spotted in 1957 in Hunsdorf, along the river Alzette. Currently it is only observed sporadically across the Grand Duchy, and is also present in the bordering regions of France (Moselle & Chiers rivers) and Germany (Saar). It is feared that it could spread to other rivers in Luxembourg.

The species' overgrazing "can cause local extiction of acquatic plants, the destruction of weedbeds and of nursery fish areas" according to natur&emwelt in Luxembourg. It burrows into riverbanks and can affect the flow of small rivers and streams, as well as the habitats of marshbirds.