A large part of the Netherlands consists of wetlands; the Dutch mted land from water but created also water in reclaimed land. This activity became clearly visible in the polder landscape with its numerous canals, ditches and shallows lakes. Rivers were regulated and also most of the brooks on the higher sandy soils. Estuaries were cut off from the sea by dams which prevent normal tidal effecrs and sea water inmsion. The original flora and fauna was and is affected by these works so that natural hydro-environments are rare in the country. Still existing "natural" hydro-environments survive by the gratitude of specid planning and managing water and land, but everywhere water quality is influenced by man, even the quality of groundwater