Chiang Mai Journal of Science

 An investigation of the distribution of toxic algae in Khlong Rangsit, Prathumthani Province was conducted from December 2007 to May 2009. Seven divisions and 88 species of phytoplankton were found. Seven species of toxic algae, namely Anabaena circinalis, Cylindrospermopsts phillippinensis, C. raciberskii, Microcystis aeruginosa, Oseillatoria limasa and Oscillatoria tenuis, were found. Futhermore, toxic algae, namely Microcystis aeruginosa, was found to be widely distributed at many of the sampling sites and usually formed as scum on the water’s surface, of which the highest cell density was recorded as 4864111 cellL^-1. The highest biovolume of phytoplankton were Oseillatoria limasa and Oscillatoria tenuis, respectively. For microcystin analysis, the microcystin RR type was detected in high abundance, but microcystin YR type was not found to be present in any of the samples. The highest values of microcystin RR and microcystin LR type were 0.85 mgmL^-1 and 0.53 mgmL^-1, respectively. Based on the standard for surface water quality of Thailand, the water of Khlong Rangsit was classified in the fourth category and could be used for household consumption after going through disinfection and special water treatment processes.