Records of fossil akinetes of Aphanizomenon and Anabaena (Cyanobacteria) in the laminated sedimentsof Lake Gosciaz are interpreted. Increasing human impact in the catchment area of the lake (as can be interpretedfrom the pollen records of human impact indicators) apparently had its effect on the trophic conditions of the lakewater: from ca. 1000 AD on fosil akinetes of Aphinizomenon and Anabaena are present in enormous quantitites inthe sediment. The increases of the Cyanobacteria are interpreted as the effect of an intensiication of farming andland fertilization in the area around Lake Gosciaz, causing eutrophication of the lake. Phosphorus enrichment formeffluent and excreta in the catchment area of the lake at times will have become so high that N-limited growthconditions occurred. In such conditions Cynoobacteria capable of nitrogen fixation (namely Alphanizomenon andAnabaena) could bloom. The deposits of the last ca. two centuries are characterised by the successive appearanceof Pediatrum boryanum, Tetraedron minimum, Coelastrum cf. reticulatum, Botryococcus, Scenedesmus, Spirogyra,Gloeotrichia and Staurastrum manfeldtii, whereas Cyanobacteria show a decline. This phytoplankton successioncould be interpreted in terms of competition for nutrients and light: higher eutrophication levels and higher turbiditycaused a decline of available light, and as a consequence less enegry was avilable for the energyu consumingprocess o nitrogen fixation by Aphanizomenon and Anabaena.