12 or 25 hours continuous observations were made for the variations of nutrients and chlorophyll ${alpha}$ with tidal cycle at a fixed station located at a mid-channel of the Masan Bay. High nitrate concentrations were observed at the time of low tides whereas high phosphate concentrations at the time of high tides. It is suggested that anoxic bottom waters could also be the possible source of high phosphates in the outer bay. Chlorophyll ${alpha}$ concentrations were related to the nitrates in April and to the phosphates in June and August. The possible role of growth stimulators in causing the extensive blooms of red tide organisms is suggested.