These are supplement data for the article "The impact of OTU sequence similarity threshold on diatom-based bioassessment: A case study of the rivers of Mayotte (France, Indian Ocean)", in preparation The folowing files are available: Supplement 1. Map of Mayotte with the sampling sites and the rivers. Supplement 2. rbcL primers, reaction mixture, and conditions used for the PCR of the 312-bp rbcL fragment. The information provided is for a single reaction with a final volume of 25µL. Supplement 3. The 20 fastq files containing the demultiplexed DNA reads. Supplement 4. Number of sequence reads for each sample before and after the trimming procedure. Supplement 5. The 20 OTU lists, corresponding to the 20 SSTs, including the number of DNA reads within the 90 samples and their assigned taxonomy. Supplement 6. Sampling site description with sample codes, names of rivers, year, number of raw DNA reads and GPS coordinates. Supplement 7. Values and summary statistics for the environmental variables. Supplement 8. The script used in Mothur for the bioinformatic analysis from trimming to the used OTU lists.