At Gappo beach, Aomori City, sea water is being contaminated by polluted water from river stagnating in the rear of the offshore breakwaters constructed in front of the beach. This report describes the results of hydraulic model tests conducted in order to find improvement-measures of it. The scale of model is 1/100 horizontally and vertically, water level the mean water level, tidal currenta constant current and wave a small wave in summer. Current patterns and dye dispersion are measured through tests with improvement measures. Construction of a jetty at the mouth of river, removal of some parts of offshore breakwaters and addition of a pump circulating the sea water have been suggested as the improvement-measures.