APHANIZOMENON-OVALISPORUM (FORTI) IN LAKE-KINNERET, ISRAEL

The filamentous cyanobacterium Aphanizomenon ovalisporum was observed for the first time in Lake Kinneret in August 1994 and formed a promin ent bloom from September through October. Aphanizomenon ovalisporum re appeared in diminished amounts in the summer and fall of 1995. These e vents are the first record of significant quantities of a potentially toxic nitrogen-fixing cyanobacterium in this lake. No definite provena nce of inoculum has been identified, although A.ovalisporum was also o bserved in a newly reflooded area (Lake Agmon) in the catchment. Unusu ally high water temperatures and low wind inputs were observed prior t o and during the A.ovalisporum bloom period. These, together with poss ibly enhanced availability of phosphorus or other growth factors, may have contributed to the cyanobacterium growth in 1994. Phosphorus limi tation, as indicated by high cellular alkaline phosphatase activity, t he onset of stormy conditions and a fall in water temperatures led to the demise of the 1994 bloom. Although the A.ovalisporum bloom in 1994 had no serious direct impact on water quality, the continued presence of a potentially toxic cyanobacterium in Lake Kinneret, a major natio nal water supply source, is a cause for serious concern.