Zasavica is a 33.1 km-long, slow-flowing river on the southern edge of the Pannonian plain. It has been a protected natural asset since 1997, and has great value as a natural aquatic habitat. In the period between 1998 and 2010, intensive studies of the aquatic vegetation were carried out. The comparisons of results gained at the beginning of that period with those from the end, show significant differences in species composition, spatial distribution, and diversity analyzed through species richness, Shannon’s diversity index, and evenness. [Projekat Ministarstva nauke Republike Srbije, br. III43002]