During September 1993, the water in Haifa Bay, Israel, turned brown and turbid, and a phytoplankton bloom was observed. Preliminary examination of the seawater showed very high concentrations of o-phosphate, nitrate and dissolved oxygen, and high pH values. In order to investigate this unusual occurrence and determine the environmental conditions that allowed for its development, the chemical and physical characteristics of the water column were measured, one during the unusual bloom in September and one during October 1993, after the bay appeared to have returned to normal. The distribution of nutrients and chlorophyll-a at the surface corresponded closely to that of the salinity and temperature, with high concentrations in the region close to the Kishon estuary, decreasing northward and westward. It was possible to determine that the Kishon river was the main source of the nutrients to the bay, originating from the effluents discharged into the river by a sewage treatment plant and nearby industries. During September, the input of nutrients from the Kishon to the bay was twice as in October, and this, together with favorable hydrographic conditions, most probably caused the unusual extensive phytoplankton bloom.

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