In this report, we have tried to find a relation between the invading of some woody species in wet-meadows at the Dalälven river and the annual water-fluctuations of the river. Allthough it is clear that the flooding of the wet-meadows must have an impact on the vegetation, we did not find the expected clear relation. We found however, some support for our hypothesis, but we also found some contradicting facts. For instance,the wet period from 1980 to 1983 has given very few numbers of both, birches and pines. The period from 1974 to 1979 had mainly dry years and during this period large numbers of birches have established. But the year of 1977 with extremly high spring-waterlevels has also given high numbers. However, 1977 had a rather normal second half of the growing-season. From this we might draw the conclusion that high waters in the early part of the growing-season have less impact on, at least, birches. A factor, which is of importance is light. Although there is much light in wet-meadows, there is a thick layer of litter (mostly died-off grass, herbs). This thick layer could be a barrier for seedlings in getting enough light in their first growing-season. What we see in the field, is that most trees have established on top of tussocks (what we called,position tree), to be able to get more light. Other important factors are: the daily temperature and rainfall in the growing-season, together with wind forming the micro-climate in which the seedings have to develop. Very hot summers with no wind or no rain, could be fatal to seedlings that stand in unsheltered positions. Another factor is competition with other, perhaps more successful, plants, especially in the first years, this could be important. The final conclusion must be a complex of factors, of which water-level is only one, determine the establishment and survival of trees in the wet-meadows. The invading of wet-meadows by tree-species can be viewed upon as a natural process, allthough it proceeds very slowly. In the last decades, however, it seems that this process has increased it`s speed, which still could be due to moderation of annual water-leveles by hydro-electric-powerstations, among other factors.