Abstract: The seasonal dynamics and the net growth rates of the planktonic freshwater cyanobacterium Cylindrospermopsis raciborskii were monitored in a shallow artificial pond in northern Taiwan from February 2010 to January 2011. C. raciborskii was present in the pond throughout the study, and its abundance was positively correlated with water temperature. The net growth rates of C. raciborskii displayed no clear seasonal pattern, whereas the highest value (0.184 d−1) was observed in early July when the water temperature sharply increased to the annual highest level. The rapid growth of C. raciborskii led to bloom formation, which persisted over the summer months (July and August). Dilution and washout of trichomes by rainfall significantly affected the dynamics of C. raciborskii, including leading to the termination of a bloom.