This paper presents an assessment of the ecological conditions of various small and medium-sized lowland watercourses of Lower Silesia, determined in part by using aquatic macrophytes as biological indicators of the health and condition of such watercourses. Research was based on the German PHYLIB system (The German Assessment for Macrophytes and Phytobenthos), which determines ecological status based on the RI index (Reference Index). Field studies were conducted during 2007-08 on various watercourses. Research included identifying the species of aquatic macrophytes found in the streambed, as well as determining the degree of coverage; on this basis the RI index was calculated. We found the ecological status of most of the tested sections to be defined either as poor (Class 4) or moderate (Class 3). Research found that the type of streambed had little effect on the number of aquatic macrophyte species or on the ecological condition of the watercourse. We observed that time played a critical role in affecting these indicators, especially over the period that elapsed from the moment when human technical interference was first observed.