In the coldest and driest season of the year (i.e., February 3 and 4, 1968) measurements were taken on water temperature, chlorinity, pH and phosphate-P, ammonia-N, nitrite-N and nitrate-N contents of sea water off the estuary of the Ashida River, occupying 14 stations both at a high and a low water. The water temperature was within a range of 6-8°, its vertical variation being very slight reflecting the vertical circulation of water due to convective cooling. Chlorinity also demonstrated a slight vertical variation due to the same cause in all places except in the close vicinity of the river mouth and in the waste water discharged from a chemical plant. Normal pH values were encountered everywhere except in the vicinity of the chemical ...