|To elucidate the influence of snowmelt flood event on the habitat of juvenile fish of salmon and sandfish、 field observation of water quality were conducted in the Mukawa coast、 the Pacific Ocean of northern Japan. The MODIS Chl-a showed the Chl-a increased by snowmelt flood after the spring plankton bloom in the Mukawa coast. As same as summer season、 the primary productivity in bottom water was limited by scattering of light by suspended sediment of snowmelt flood in spite of sufficient nutrient for the aquatic ecosystem. However、 the primary production was still higher than that after summer flood because of vertical mixture by the surface cooling at nighttime. This high primary productivity seemed to bring the increase in zooplankton、 which can provide the better food environment for juvenile fish.