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In the aquatic environment biology and hydrology should assist each other in explaining the establishment, fluctuation, and limitation of the aquatic vegetation. However, the description of running and still waters by hydrology and habitat hydraulics, and the description of the aquatic vegetation, and its dynamics, rarely lead to results on a comparable scale. This is due to some intrinsic methodological features of both sciences, but also due to the fact that there is not much effort to find a common basis of scale. This is to no surprise because most of the time a hydrologist, and vice versa a biologist, tries to solve problems on his own, rarely calling for a partner from the other field. In the personal view of a biologist aspects are pointed out which may lead to a better interpretation of biological processes through habitat-related hydrological and/or hydraulic assessments. The terms macrophytes, environment and success are defined first. The function of macrophytes as a part of the aquatic ecosystem is explained, and related to important environmental factors. Examples are given for water flow as the most prominent abiotic factor. With respect to water flow and light the assessment of these parameters should be more detailed regarding space and time to be relevant to the scales in which aquatic plant life takes place. With regard to nutrient assessment spatial resolution is not as sensitive an issue as long as the water body, and not the interstitial, is concerned. However, any increase in detail will considerably raise the effort, and the cost, of data acquisition. Measuring plant “success” with physiological methods and biometrics can be too complicated for in situ work. Methods fitted to single species spatial development may cope with such problems and GIS is the tool to choose in such cases. Finally the urgent need to find common scales among hydrologists and biologists is addressed.