AbstractQuestionWhat are the changes in mineral‐rich fens (H7410A) after 25 yr of improved surface water quality in a national park?LocationStobbenribben floating‐fen complex in National Park Weerribben‐Wieden, the Netherlands.MethodsBryophyte species composition, peak above‐ground biomass and vascular plant nutrients, as well as electrical conductivity of various layers in the peat were measured between 1988 and 2013.ResultsThe eutrophic moss Calliergonella cuspidata clearly decreased in aerial extent over the 25‐yr study, especially near the ditch supplying base‐rich surface water to the fen. In contrast, the characteristic rich fen species Scorpidium scorpioides expanded locally near the ditch. In the rich fen zone, peak above‐ground biomass decreased from ca. 1000 to 250 g·m−2. Also, foliar N:P ratios in vascular plant tissues increased from 16 to more than 22 g·g−1, which clearly point to lower P availability over time. Improved surface water quality probably also promoted persistence of rich fen habitats in a different way. A large part of the rich fen peatland in 1988 changed into Sphagnum peatland by 2013, probably due to the reduction of base‐rich water from below the floating root mat. This mat had become ca. 35 cm thicker in the past 50 yr. However, in areas closer to the ditch, rich fen species persisted, due to inundation with base‐rich water during high water periods. Base‐rich water probably no longer comes to the surface through the floating root mat, but more likely from the ditch.ConclusionsWater quality improvement can be important in the long‐term re‐establishment of target fen species. Also, local inundation can be helpful if regional groundwater access becomes limited. In the national park, rich fens are more threatened than Sphagnum peatlands. This study suggests that the rich fen stage can be maintained, and succession towards Sphagnum peatland prevented, with occasional inundation with high pH, nutrient‐poor water.