Toyama Bay, a semi-enclosed water body on the northern coast of Japan with its averaged water depth at 600m, has a steep bottom topography from the coast toward its central deeper part. It is known that there are basically three water masses in the bay: the Coastal Surface Layer Water, Tsushima Warm Current（TWC） Water and Japan Sea Proper Water from its surface to bottom. The present study describes the seasonal variation of the water masses and current structure in the bay, based on oceanographic observations, which include temperature and salinity with a CTD （Conductivity, Temperature and Depth profiler） system and current velocities with ADCP （Acoustic Doppler Current Profiler） mounted onboard the training ship Wakashio-maru that belongs to Toyama National College of Technology（ TNCT）. The data obtained in summer of 2005 and 2012 were used in this study. During the above cruses in summer we often observed an anticlockwise eddy with its diameters of about 20-30miles（37- 56km） in the inner part of the bay. Based on the series of the present observations, it is suggested that the anticlockwise eddy in summer is generated and maintained by TWC flowing into the bay along the coast of Noto Peninsula. Summer oceanographic conditions of smaller internal radius of deformation and the larger river water discharge in comparison with winter season enhance the formulation of this eddy.

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