The results of this study clearly demonstrate that MCs were detected from all four recreational water reservoirs. The highest MCs content and also Microcystis sp. biovolume were found in Bueng Nong Khot, with negative correlation. Based on the morphological characteristics and 16S rRNA analysis, the dominant bloom-forming species in Bueng Nong Khot was identifi ed as M. aeruginosa. However, the potentially toxic tropical cyanobacterium, Cylindrospermopsis sp. was found as the dominant cyanobacteria in Bueng Kaen Nakhon, Bueng Thung Sang, and Bueng See Than. This finding suggests that many cyanobacteria which are growing in water reservoirs may constitute a source of cyanotoxins. To prevent intoxications continuous monitoring of these reservoirs is strongly recommended.This has to be taken into account because human health
and animal hazards may be involved.