A Freshwater Red Tide on a Water Reservoir

Abstract

A long-lived, heavy freshwater red tide of Pyridinium occurred in a newly built water supply reservoir, between late February and late May, 1972 and 1973, starting and spreading from the entrance region. The densities of the alga reached at least 9.3 x 104 cells per ml and at least 2, 700 μg chlorophyll- a per liter at a wind drift. The red tide is attributed to the increase of solar radiation, the hardness of water and the sewage drains from towns and croplands. The water mass containing a dense algal bloom was an excellent receiver of the solar radiation. This flagellate acted as an accumulater of nutrients at the entrance region of the reservoir.