A current and water quality observation system consisting of drift type buoys equipped with differential GPS (DGPS) was developed. This report presents the outline of the system that was developed and the results of the verification of the field observations. The system was used to perform current observations along the coast of the Ariake Sea to measure the current and quality of water (salinity concentration and turbidity) carried by the current downstream from a tide gate. The results showed that the system enabled to perform current and water quality observations with accuracy for practical use. The system showed the following characteristics: 1) It enabled to determine easily the path line and the velocity of a surface current; 2) The method was effective for analyzing currents where flowing fresh water converges and where dangerous conditions prevail; 3) The buoys could be equipped with a variety of water quality observation devices; and 4) The risk of observations performed during flooding and under other dangerous conditions could be reduced. The system was found to be effective for performing easily high precision observations of currents and water quality over a wide area extending from river mouths to the open sea.