Background Microtus oeconomus subsp. arenicola is a subspecies of the root vole that is endemic to The Netherlands and is listed as a priority species in Annex II of the Habitats Directive. The root vole lives in wet reedlands and grasslands along lakes and rivulets. It is found mostly on the Wadden Island of Texel, where it thrives thanks to a lack of competitors like the common mole (Microtus arvalis) and the field vole (Microtus agrestis). Isolated populations also exist in other parts of the country, but these are rapidly disappearing due to the shift towards more intensive farming practices and a permanently stable groundwater level, which has encouraged other voles to move in. Unable to compete with them, the sub-species population is now at an all-time low. Objectives The project aimed to increase the optimal habitat of the root vole in its core area in the province of Friesland at a site called the Alde Feanen (the old peatlands) managed by It Fryske Gea. Here, the species still occurs but is vulnerable because of its limited population size. The project would strengthen and develop a healthy core population, by recreating a suitable habitat on recently acquired farmlands and by installing a variable water-level management regime in the existing nature area. This cyclical water management would allow the water level to be decreased inside one area (Jan Durkspolder) where it is currently too high, while increasing the water level in another area (Wolwarren), so to eliminate competition of the field vole. Such actions require significant structural engineering works such as excavation, filling in of existing ditches, reconstruction of a micro-relief, strengthening of the canal banks in the surrounding area and securing roads and buildings. A secondary objective was to enable other rare species to benefit from the project. This aims applies mainly to the animals found in marshland vegetation, such as the bittern. The project would be publicised through sign-posting, an exhibition and publications. Results The most important measures taken were raising the water level and increasing water-level dynamics. On top of the natural seasonal fluctuation (high levels in winter, low levels in summer) in the two lower parts Westersaning and Jan Durkspolder, water level rotation was put into effect. As a result, two areas will be managed as marsh for a number of years (dry period) after which they will be inundated for several years (wet period). In the years with low water levels marsh plants and willows will germinate on the dry slicks. During wintertime these seedlings will partly be lost again; in spring the remaining one can develop further. Most plants will be lost again when the dry period is replaced by the wet period. By applying this water-level rotation, the two areas will complement each other continuously. As a result, together they will always contain suitable habitats for the Dutch root vole and other waterfowl species.