In this paper investigations of biomass of red head grass Potamogeton perfolitus L. from Lake Ohrid were presented. The material was collected from 2 localities along the Ohrid Lake's coast (Grasnica and Kaneo), where anthropogenic influence is different expressed. The results from the investigations show that there are differences in biomass between investigated localities.

In order to determine the dynamic of biomass of stoneworts from Lake Ohrid as a function of the trophic state of the water, we collected samples from four different localities. The localities Sveti Stefan and Mazija, were characterized by oligotrophic state of the water, while the other two Grasnica and Daljan were characterized by eutrophic-mezotrophic water quality. The stoneworts samples were taken from 4-5 different depths from each investigated locality. The results of our investigations have shown that higher trophic level of the water from the littoral region of the localities Grasnica and Daljan (especially in the points of inflow of river Grasnica and Daljan) decreases the amount in stoneworts biomass compared with the biomass of stoneworts collected from the first two localities that characterizes oligotrophic character of the water.