Diatoms are unicellular algae particularly sensitive to changes that affect their aquatic environment. This is why they are used as bioindicators for the biological monitoring of water quality. However, their microscopic identification in river samples requires a lot of time and skill. Biologists from the University of Geneva (UNIGE), Switzerland, have succeeded in establishing a water quality index based solely on the DNA sequences of the diatoms present in the samples, without needing to identify each species visually. This study, published in the journal Molecular Ecology Resources, presents a revolutionary tool to process a very large number of samples in parallel, allowing wide coverage of the monitored sites in a reduced time and at a lower cost.