When industrial wastewater containing fluoride runs into the ocean, approximately 0.1ppm of F$^$-/ will react with seawater and will be eventually lost, and the remaining F$^$-/ can be determined withe the ALC. Therefore F$^$-/ is eligible to be used as a tracer of pollutant which contains fluoride. Determination of F$^$-/ in the seawater with the Dotite reagent, Alfusone, has been made by the following method: To 10 ml of water sample, 1 ml of buffer solution (pH=4.0), 8 ml of acetone, and 1ml of 10% Alfusone were added and diluted to 25ml with distilled water. After 20 minutes the absorbance at 620 nm against a reagent blank was measured. The distributions of F$^$-/ in Jinhae Bay has been made on the basis of water samples collected from 103 different sampling stations occupied in Jinhae Bay. The water samplings, three in the spring tide and two in the neap tide, were taken from surface layer during the flood and ebb tide periods respectively. The average concentration of F$^$-/ in the bay, except the area to which the wastewater runs off from the Chemical plant, was 1.45 ppm(1.07-6.33ppm), and that of F$^$-/ in the plant effluent was 330ppm, occasionally up to 562 ppm. Thus high levels of F$^$-/ in the bay are strongly correlated to the amount of effluent from the plant, and waters of Jinhae Bay contains at least 0.13% of the plant effluent.