AbstractThe unity of the structure, function and performance of an ecosystem and the importance of the biotic factors are represented by the example of the storage reservoir. Besides the morphometric relation of the trophogenic layer to the tropholytic one, the effect of the stability and mixing depth as well as of the o‐PO4content on the phytoplankton development is demonstrated. The secondary production of zooplankton is described with respect to its interaction with phytoplankton and the specific relations between the available food and the greazing pressure of predators for the structure of populations ofDaphniaare treated in particular. The practical consequences resulting from abiotic and biotic structural features for water quality are pointed ou