Abstract
A freshwater red tide of Uroglena americana usually occurred after the continuation of windless weather for several days and disappeared after stormy weather.
Three typical distribution patterns were obtained as the results of observation of the distribution of temperature and chlorophyll. In Type I, the vertical distribution of both chlorophyll and temperature were uniform from the water surface to the bottom. In Type II, the peak of chlorophyll concentration was found at the depth of 2-3 m. In Type III, the maximum concentration of chlorophyll in the vertical distribution was found at the surface of lake water where water temperature was remarkably high compared with that of the deeper water. A dense accumulation in the horizontal pattern of colonies of U. americana was found in the area where the temperature of surface water was relatively low, in the case of Type II. On the contrary, with Type III, the population maximum was found in the area where the water temperature was relatively high.
