Nature in Flanders these days suffers from severe negative impacts caused by acidification, eutrophication and many others. Line shaped elements like watercourses are very vulnerable for these degradations. They run through as well natural and semi-natural areas as through or around villages and towns and so they have a greater risk to become degraded.In the Mina-plan, the plan for Environment and Nature, the Flemish government has laid down many objectives for nature. One of these is the maximal conservation of the present natural values for the next generation. Reference values are needed for controlling this and will be determined in this study.Particularly, we will determine “target values” and marginal values of non-biotic parameters, which are relevant for acidification, dehydration and eutrophication. The target values determine the state of the environment in which a type of nature will develop in optimal conditions while the marginal values mark the range in which that type of nature still survives, but not optimally. In the ideal state, we must reach these values in our watercourses. With them, we can link environmental quality with nature targets. Also we can evaluate the quality data of the FEA (Flemish Environment Agency) directed towards nature.