A type of dinoflagellate called Peridinium bipes f. occultatum is causing freshwater red tides in many reservoirs in western Japan. The researchers studied the physiological characteristics of this species to understand why it forms red tides. They found that P. bipes prefers high light intensity compared to other similar species and can thrive in low nutrient conditions. This ability to grow in high light and low nutrient conditions is likely why red tides form in many reservoirs. The maximum growth rate of P. bipes is lower than other species it coexists with, indicating it may not always have a competitive advantage in growth.