The German Society for Limnology (DGL) in cooperation with the Institute of Zoology at the University of Cologne cordially invites to the 38th annual conference of the DGL in Cologne from September 18th to 22nd, 2023. The motto of the conference "Endangered biodiversity of freshwaters" is and remains more relevant than ever. Man has changed nature almost everywhere on earth, this applies in particular to water. The destruction of natural water bodies, pollution and global warming have led to a decrease in species numbers and habitat quality almost everywhere. Far-reaching measures against these negative developments are urgently needed. Although humans depend on numerous ecosystem services, these are increasingly threatened. The IPCC reports of recent years also identify rivers and lakes as habitats that are particularly endangered by climate change. Resulting changes in flora and fauna can now be recognized using modern genomic studies. At the conference we want to explain and discuss the current status with a few plenary lectures and your lectures and posters. We also invite poster and talks on current and trend-setting projects ranging from topics like classical limnology, organismic biology and ecosystem research to innovative, interdisciplinary approaches in basic research and practice. Conference website is at https://www.dgl-jahrestagungen.de/