The project involves the removal of drainage from a wet grassland at the head of a small Breton coastal river watershed in an area subject to nitrogen pressure. Located at the bottom of an hydromorphic valley, the Coat Carriou meadow has been drained by two ditches to allow the plot to be mowed. Collecting runoff from the hillside, the two ditches caused a short circuit in the meadow, leading the nitrate-laden runoff directly to the river stream. The two drainage ditches were filled in with the aim of eliminating the short circuit, allowing all water flowing to spread over the meadow. The aim was to improve the purifying effect of the grassland on the waters from the hillside, while maintaining agricultural activity. The short circuit has effectively been eliminated, allowing all the water on the slope to pass through the wetland where the purifying capacities make it possible to remove all the mineral nitrogen present in the water. As the purification capacities were already optimal before the work, they were not improved, but all water can now be purified. The reduced bearing capacity allow to mow the meadow only in dry years. It has been included in the grazing path of a herd of brittany pie-noir cows, able to graze wet grassland.