Abstract: The climate at the Techi Reservoir catchment is suitable for fruit,vegetable,and tea cultivation.So,there are many fruit,vegetable,and tea fields located in the upper stream of the Techi Reservoir catchment.The fertilizers applied are thus washed into the Techi Reservoir during heavy rains.These fertilizers contain vast amounts of nitrogen and phosphorous nutrients,which support the growth of dinoflagellate Peridinium bipes.The dinoflagellate Peridinium bipes cells increase rapidly and as a result Peridinium bipes algal blooms occur.Conventionally,large spatial scale algal bloom studies are conducted using boats and point sampling.This is expensive and time consuming.Remote sensing data can acquire temporal,large spatial,and vast spectrum data and also track the past data.Remote sensing,which quantitatively measures the light reflected from the surface of the earth,is a powerful tool for studying regional-scale aquatic ecosystem dynamics.In this study,Landsat TM data were used to monitor dinoflagellate blooms in the Techi Reservoir with supervised classification in 1995 and the predicted accuracies for algal blooms reached above 87.5%.From the classification results,dinoflagellate blooms were predicted most serious in summer and smallest in winter.The phenomenon was associated with catchment management.The catchments are located in the upper stream of the Techi Reservoir.The results afforded us the entire algal bloom information for the Techi Reservoir instead of the conventional point data.The algal bloom areas and degree of potential seriousness were defined in this study.