design: The extraction and purification of environmental DNA was performed using the Sorb-GMO-B kit, with DNA concentration quantified fluorometrically on a Qubit 4. The V3V4 region of the 16S rRNA gene was amplified using cyanobacteria-specific primers (CYA359F/CYA781Rd) in a 25-cycle PCR protocol. Subsequently, the PCR products were purified with XP Beads, and libraries were prepared and indexed according to the Illumina 16S Metagenomic Sequencing Library protocol using Nextera XT indexes. The final sequencing was performed on an Illumina MiSeq platform using the MiSeq Reagent Kit v2 (500 cycles) to generate 250 bp paired-end reads.