Since the first reported Paralytic Shellfish Poisoning case in Bolinao, Pangasinan in 2002, monitoring efforts has been directed toward the determination of the presence Alexandrium spp. in the area. Data on the elaboration of the identity of causative organism and seasonality including spatial distribution have been fragmented and lacking despite the poisoning threat it can cause. Phytoplankton sampling was conducted for 16 months within two years in Bolinao, Pangasinan. There were 72 phytoplankton species identified in Bolinao, Pangasinan from January 2010 to August 2011 comprising of 49 dinophyceae (55%), 34 bacillariophyceae (38%) and 6 other plankters (7%) belonging to cyanophyceae, raphidophyceae, dictyochaphyceae and spiroteachea. Blooms Alexandrium spp. mostly in the fish farming sites located in northern part of the channel was detected during the Trade winds at 2.93 x 105 cells L-1 (May 2010), 1.9 x 104 cells L-1 (March 2011) and 5.8 x 104 cells L-1 (May 2011). Intensive and extensive monitoring efforts which include phytoplankton sampling and shellfish toxicity analysis should be done more regularly especially in months when Alexandrium spp. begin to proliferate ie January to May.