Parisian gutters harbour an impressive variety of micro-organisms. Scientists have studied biodiversity in street gutters, and compared it to biodiversity in sources of non-potable water. They analysed around a hundred samples from locations throughout Paris, and found 6,900 potential eukaryote species. Much of this great biodiversity consists of microalgae in the diatom group, alongside other unicellular eukaryotes such as amoebas, alveolates and rhizari, as well as fungi, sponges and molluscs. Scientists have developed the hypothesis that these complex biological communities could be harnessed to treat stormwater and urban waste by helping to break down solid waste and other types of pollutants.