Harmful Algal Blooms (HABs) of Alexandrium catenella have been documented in Puget Sound, Washington State, for over 60 years. A. Catenella produce a suite of potent neurotoxins, known collectively as Paralytic Shellfish Toxins (PSTs), that accumulate in filter feeding shellfish. Consumption of contaminated shellfish poses a significant threat to human health. Data from the Washington State Department of Health's (WDoH) Biotoxin Program were used to determine variability in PST behavior and determine if local and/or large-scale climate factors contribute to the development of events at Sequim Bay in Puget Sound. This embayment has been identified as a “hot spot” in Puget Sound for shellfish toxicity. Correlation analyses of seasonally averaged PST levels in Blue Mussels, Mytilus edulis, with local environmental conditions revealed significant and robust relationships with streamflow and sea surface temperature (SST). This indicated that low streamflow and SSTs in the fall may increase PST risk. A high frequency event analysis of PST variability on a daily timescale was conducted for exceptional toxic events in 1992, 1993, 1994, and 2000. This analysis focused on the 14 days prior to the events to determine a combination of favorable conditions that may initiate and sustain high toxicity. Of the preceding favorable environmental conditions, streamflow and air temperature contributed most to the development of toxic events. Thus, warm temperatures and low streamflow conditions may stimulate bloom growth and determine conditions for high shellfish toxicity during fall months. We hope to apply these findings to better predict PST risks in Puget Sound.