[in Dutch with English abstract: ] Cetraria islandica is known from three localities in the province of Overijssel. A survey initiated by the provincial government revealed that at two of them the population is at danger. The largest (Lemelerberg) population is managed by a nature conservation organization (Landschap Overijssel), the two smaller localities were not managed with a lichen conservation aim. In consultation with the landowner’s ecologist, at one site a simple fence was placed to protect the single thallus at that site from trampling. At the other site a group volunteers, removing birch etc., was joined to help with sod cutting, in order to protect and possibly enlarge that specific spot.