Preliminary Assessment of the Ecological Status of Some Tributaries of Lake Ohrid (Macedonian Part) Based on Diatom Community according to the Water Framework Directive

The main aim of our study was to assess the water quality in the Lake Ohrid watershed (Macedonian part) based on diatom indices (Trophic Diatom Index and Saprobic Index) as defined by the EU Water Framework Directive. In addition, dissolved oxygen, dissolved organic matter and total phosphorus were measured. The study was carried out along the following tributaries of Lake Ohrid: Sateska, Koselska, Velgoshka, Rachanska and Cherava rivers and the Canal Studenchishta, as well as the outflow Crni Drim/Drini River. The Saprobic Index ranged from 1.6 (oligo-beta mesosaprobic class) to 1.9 (beta mesosaprobic class) registered in the inflow of the Cherava River. The Trophic Diatom Index ranged from 1.6 (mesotrophic class) in the upper flow of the Sateska River and the middle flow of the Koselska River to 2.5 (eutrophic class) in the inflow of the Velgoshka River. The rivers Velgoshka and Cherava showed the highest pollution and negative influence on Lake Ohrid.