Cyanobacteria (blue green algae) are ubiquitous as they can be found in almost every habitat, from oceans to fresh water, bare rock and soil. A study about the diversity of marine cyanobacteria was carried out at three selected razor clam production sites namely Asajaya, Bako and Buntal. There were six genera of cyanobacteria found during the namely Anabaena,
Chroococcus, Microcystis, Oscillatoria, Spirulina and Synechocystis. Four out of the six genera can live either in water body (planktonic) or on the surface of substrate (benthic). Those cyanobacteria were Anabaena, Chroococcus, Microcystis and Oscillatoria. Three out of six cyanobacteria genera were , known to be potential toxin producers namely Anabaena, Microcystis and Oscillatoria. A study of Oscillatoria growth was also carried out to see the growth rate of this genus. Marine cyanobacteria genus Oscillatoria was successfully isolated in BG11 medium for marine cyanobacteria with continuous light in growth chamber with temperature around 29°C. The culture showed maximum cell density at the fifth day regardless whether the initial density 0.4 x 104 cells/ml, 1.0 x 104 cells/ml or 1.2 x 104 cells/ml.