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Harmful cyanobacterial blooms have become increasingly common in freshwater ecosystems in recent decades, mainly due to eutrophication and climate change. Water becomes unreliable for human consumption. Here, we report a comprehensive study carried out to investigate the water quality of several Campina Grande reservoirs. Our approach included metagenomics, microbial abundance quantification, ELISA test for three cyanotoxins (microcystin, nodularins, and cylindrospermopsin), and in vivo ecotoxicological tests with zebrafish embryos. Cytometry analysis showed high cyanobacterial abundance, while metagenomics identified an average of 10.6% of cyanobacterial sequences, and demonstrated the presence of Microcystis, Cylindrospermopsis, and toxin coding genes in all ponds. Zebrafish embryos reared with pond water had high mortality and diverse malformations. Among the ponds analyzed, Aracagi showed the highest lethality (an average of 62.9 +/- 0.8%), followed by Boqueirao (lethality average of 62.5 +/- 0.8%). Here, we demonstrate that water from ponds undergoing extremely drought conditions have an abundance of potentially harmful cyanobacteria and their toxins. Our findings are consistent with a scenario in which polluted drinking water poses a great risk to human health.