Summary:

This paper presents the evaluation of the risk factors in the watercourses which will be regulated or maintained in the future. The analysis concerns one of the components of the ecological risk – the risk of the qualitative and quantitative changes by the aquatic plant communities. The basis of the analysis were field studies, which were carried out during the years 2007-2008 in six lowland water-courses in the Lower Silesia. On the river beds there were executed regulation or the maintenance works. The field studies comprised identification of aquatic plant species and es-timation of their cover-abundance. For the abundance analysis we used the Braun-Blanquet Scale. At the natural transects the number of aquatic plant spe-cies ranged from 4 to 7, and abundant from 5 to 100% of the bottom surface. At the altered stretches the number of aquatic plant species ranged from 0 to 5. The plant abundant did not exceed 25% of the bottom surface. On the ground on these dates were prepared a maps of ecological risk, which can be used in planning and execution on watercourses regulation and maintenance works.