The results of an investigation carried out during August-2013 to July-2014 on cyanobacteria blooming species and investigation of the water quality parameters from Muttukadu estuary. The water samples for plankton analysis were collected by using plankton net and the water samples for nutrients analysis were collected in the sterile plastic bottles. Microcystis aeruginosa cell density values were varied between 7.9x108 cells/l to 1.3x108 cells/l in all three stations. Arthrospira platensis cells density were varied between 1.2x107 cells/l. to 10x107 cells/l. In all three stations the Trichodesmium sp cells density varied between 4.7x107 cells/l. to 1.9x107 cells/1 respectively. Rainfall varied from 0 to 211mm. Air and surface water temperatures (°C) varied from 27.1°C to 36.8°C and 25.1°C to 35.7°C respectively. The respective salinities varied from 0 to 8.3 and the respective pH ranged between 7.15 and 8.51. Correspondingly, the dissolved oxygen content varied from 4.54 mg L-1 to 7.83 mg L-1. The content ranges of inorganic nutrients, nitrite, nitrate, ammonia, phosphate, silicate and total suspended solids(µmol L-1), range from, 7.35 to 19.34, 3.26 to 9.34, 4.28 to 20.57, 2.01 to 8.63, 50.24 to 115.34 and 93.85to 314.62 respectively. The Chlorophyll ‘a’ content was varied between 0.242 (mg/l) to 0.091 (mg/l). The seasonal distribution and abundance of cyanobacteria bloom are discussed in relation to physico-chemical parameters. Totally three cyanobacteria blooming species present in muttukadu estuary. Monitoring and assessment should be made continuously in Muttukadu estuary for to protect the human and animal health.

Keywords: Plankton; Bloom; Cyanobacteria; Nutrient; Chlorophyll.