In the present paper, the authors tried to estimate the influx loads into a double-closed bay (Omura Bay) using forty-nine scenes of Landsat5/TM from 1984 to 2000, and statistical data for many years. From the TM data, NDVI (Normalized Difference Vegetation Index) values were calculated for four seasons in each year. The outcomes without sea areas were classified into five categories, which were water region (pond, lake, etc.), forest area, agricultural land (plow land and paddy field), uncovered ground, and urban area. The influx loads were calculated from the total of surface areas of each category and the statistical data in each year. The relationship between the influx loads and the sea water quality changes of the bay was evaluated. Adequate correlation was estimated between phosphorus and nitrogen influx load, which were calculated from TM data, and the actual values of total phosphorus and nitrogen in the bay, respectively. However, in the case of COD and chlorophyll-a values, mutual relationships were not estimated from the results.