We are investigating the influence of climatic changes on the destabilization of aquatic ecosystems on the Alps. The global phenomenon of climatic change is connected with regional aspects of ecology and economy. The results will be of importance to the utilization of Alpine pastures in future. Small lakes, ponds and swamps are common on our Alps and these waters serve as indicator ecosystems. Some of them are relatively isolated hydrological systems, which are filled after the melting of snow or after rainfall and are not connected in a continuous flowing water system. The cyanobacterial coenoses in these waters are sensitive to environmental changes. Under certain climatic conditions (warm, sunny summers without much rain) the cyanobacteria (blue-green algae) may form toxins in these waters. If the environmental conditions are favourable for toxin production, these waters, which are watering-places for the cattle, may act as death-traps for the animals. It is presumed that the cyanobacterial toxins in these Alpine waters are dependent on the climatic environmental factors which are being investigated together with the toxin production. The research project is divided in three subprojects: 1) in an ecological field study on the interactions between hydrosphere and biosphere (i.e. cyanobacterial coenosis) during changing climatic conditions and during extreme climatic events, 2) in an ecophysiological laboratory study on the toxic potency of new isolates of cyanobacteria from Alpine habitats, and in a reconstruction of the environmental conditions leading to toxin production by Alpine cyanobacteria. It is also intended to work out a concept to warn against dangerous situations. Leading Questions: 1) What is the reaction of alpine aquatic ecosystems towards environmental parameters? 2) Which are the interactions between atmosphere, hydrosphere and biosphere (i.e. cyanobacterial biocoenosis) during changing climatic conditions in the central Alps and during extreme climatic events (field study)? 3) Are cyanobacteria as microscopic algae suitable indicator organisms for climatic changes?4) Which environmental conditions are leading to toxin production in 'alpine' cyanobacteria? 5) Which is the toxic potency of new isolates of cyanobacteria from alpine habitats? 6) Is the frequency of cyanobacterial toxicoses on the Alps a biological indicator for climatic changes?