In the Dutch province of Friesland large areas of Cirsio-Molinietum vegetations still existed in the beginning of the 20th century. Embankment of periodically flooded areas, lowering the water table in these new polders and using fertilizer caused a dramatic decline of this area. Nowadays Cirsio-Molinietum vegetations are extremely rare in the Netherlands and probably in the whole of Western Europe. ‘De blauwgraslanden van Akmarijp’, the largest of the remaining Dutch Cirsio-Molinietum vegetations (c. 100 ha), has from the 1950’s on been set aside as a nature reserve. The data in this paper show that the well-developed Carex panicea/Cirsium dissectum dominated Cirsio-Molinietum vegetations of the first half of this century have for the greater part changed into Caricion curtonigrae vegetations dominated by Agrostis canina and Carex nigra. The main reason of this change is the continuing lowering of water tables in the surrounding agricultural areas which in the reserve itself causes a continuing peat mineralisation and acidification of the upper peat layer. Conservation measures have been taken or are under consideration in an effort to preserve a fragment of the once abundant Cirsio-Molinietum vegetations.