The identification of species is based on the analsyis of environmental-DNA (eDNA). This DNA stems from organisms which emit cell residues via mucus, scales, faeces, pollen, etc. to their to the surrounding envrironment. These traces of eDNA are detected with universal primers or especially developed molecular probes. Based on  their DNA sequence all oraganisms inhabiting a given water body can rapidly and reliably be identified ato species level.