Šumava lakes have been recovering over the last 30 years from acidification caused by high atmospheric deposition of sulphur and nitrogen. Regeneration was manifested by decreasing acidity and increasing biodiversity (except for fish). It was temporarily interrupted by Spruce Bark Beetle (Ips typographus) infestation in lake catchments. Spruce defoliation and changes in light and humidity conditions caused enhanced mineralization of soil humus layer resulting in nitrate leaching and also partial acidification (only temporary, within a few decades the lakes will profit from the release of nitrogen from the ecosystem). and Jakub Hruška a kol.