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Environmental factors promoting algal blooms in the Lower James River estuary An intensive monitoring and mapping program was conducted in 2011 and 2012 detailing the possible triggers and temporal and spatial extent and duration of phytoplankton blooms in the lower James River estuary. Using Hampton Roads Sanitation District’s (HRSD’s) DATAFLOW platform, in situ sensors, and dock sampling, we were able to capture the initiation of an annual dinoflagellate bloom (Cochlodinium polykrikoides) bloom in late July/early August, 2011 and late June in 2012. In both years the bloom initiated in the Lafayette River, a sub-tributary of the lower James River, and extended into the Elizabeth and lower James River through August. In 2012, cell abundance for Cochlodinium polykrikoides increased once surface water temperature reached 26°C in the Lafayette River. Precipitation events introduced a freshwater influence that may have provided nutrients and buoyancy, two other factors that were key in promoting the dinoflagellate bloom. However, the frequency and timing of nutrient sampling may not have been sufficient to capture the instantaneous pulses of nutrients associated with storm events