Background and Purpose: The research in this paper are based on the study of the distribution in time and space of macrophytes along the different parts of shoreline of Gruža Reservoir and emphasize the importance of establishing relations between distribution, diversity and mass of macrophytes and the ecological conditions of the environment. Development diversity of macrophytes needs to be constantly monitored and their regulation is necessary for Reservoir conservation, especially because the Reservoir is used as a water supply for a nearby city. Materials and Methods: During the period 2004-2005 aquatic macrophytes were investigated (by the method of transects) bimonthly from May to October and results was compared with the results obtained during the research in 1986. Relative abundance was evaluated using a five degree scale. These data form the basis for the mathematical model with the following data: Relative Plant Mass for each species, cumulative Relative Plant Mass for growth forms and Mean Mass Indexes. Results: Quantitative analysis of macrophytes indicates that the morphometrical characteristics of shoreline, water depth, vegetation characteristics and nutrient pollutants play an important role in the appearance, diversity and abundance of macrophytes. Conclusions: The distribution of most aquatic macrophytes in Gruža Reservoir is heterogenous with mean mass indexes MMT (for all macrophytes in total stretches) and MMO (for stretches with their occurrence) values of different size and with low value of distribution ratio. Our results have confirmed previously set hypothesis that poor physical conditions, rather than water quality, might be responsible for restricting diversity of macrophytes. Keywords: macrophytes; horizontal extension; shoreline characteristics; distribution coefficient