Interaction among spring phytoplankton succession, water discharge patterns, and hydrogen peroxide dynamics in the Caloosahatchee River in southwest Florida

•Eukaryotic algae sharply increased when the water discharge increased.•Synechococcus and Cyanobium dominated in phytoplankton communities.•Phytoplankton dynamics influence the natural abundance of H2O2.•A H2O2 peak was found when Dolichospermum dominance was ended, and Microcystis increased.•A high correlation was found between H2O2 and microcystin (r = 0.83, p < 0.01).