To clarify the present situation of water environment in the Uchikawa River in Toyama, field observations (water quality, flow velocity distribution and plankton sampling) have been carried out continually since 2009. Water quality in the Uchikawa River had been aggravated due to the development of well-drained paddy fields and new ports in and around the river basin from 1960s. Regardless of a water reclamation program, water quality in the Uchikawa River does not show a drastic improvement.Due to the effect of purification water from the Nishi-Uchikawa River, upward flows of seawater and vertical water quality changes in the Higashi-Uchikawa River were found from the investigation results of water quality. It was also found that the spatial distribution of plankton was influenced by the water flows. The existence of both freshwater and marine (brackish) algae in the river indicates that the resources subsidizing food web are provided through the multi-directional water flow.