Over the past few decades, zooplankton populations in Lake Geneva have undergone changes in their abundance. Daphnia populations, in particular, are declining. In this study, long-term data on Daphnia abundance in Lake Geneva have shown that the most significant decline is among juveniles. Furthermore, these long-term data have highlighted a deterioration in the quality of Daphnia food as the carbon-to-phosphorus (C:P) ratio of phytoplankton has increased.

Experimentally, it was observed that Daphnia feed with difficulty on the filamentous cyanobacterium Planktothrix rubescens, which is dominant in Lake Geneva. Daphnia were exposed to different concentrations of the algae in a functional response experiment. Daphnia showed no feeding response during this one-hour experiment. However, feeding by adult Daphnia was detected during a six-hour experiment. The interaction between Daphnia and Planktothrix rubescens was recorded on video. Entanglement of the filaments in the filtering apparatus of Daphnia was observed.