High freshwater flow delivers excess nutrients to Chesapeake Bay, leading to increased phytoplankton biomass, turbidity, and eutrophication. Low flow in 2002 was associated with a persistent drought that terminated abruptly in autumn 2002, followed by extremely high flow in 2003. This large difference in flow caused improved water quality in 2002 as nutrient loading subsided, and degraded water quality in 2003 with increased loading associated with high flow. We analyzed remotely sensed chlorophyll (chl a) data using an online data analysis tool to quantify the effect of sequential low and high freshwater flow on phytoplankton biomass near the mouth of the Bay. Chl a in the study area was significantly higher in 2003 than in 2002, consistent with strong forcing by freshwater flow and nutrient loading in the nutrient-limited region of the Bay.