Milstein, A., Agricultural Research Organization, Fish & Aquaculture Research Station, Dor, D.N. 30820, Israel.
Feldlite, M., Agricultural Research Organization, Fish & Aquaculture Research Station, Dor, D.N. 30820, Israel.
Mozes, N., Agricultural Research Organization, Fish & Aquaculture Research Station, Dor, D.N. 30820, Israel.
Avnimelech, Y., Agricultural Research Organization, Fish & Aquaculture Research Station, Dor, D.N. 30820, Israel.

Factor analysis was used to identify the main processes acting in the system. Water quality was affected mainly by algae activity (first factor). Processes such as respiration, decomposition and wind action affected the degree of oxygenation (second factor). The reservoir with cages had lower algae activity and degree of oxygenation than the other reservoir and the fish pond. In the reservoir with cages, both factors had lower values in the cages than in the open water. Algae activity increased with months and from morning to afternoon, decreased with depth and was higher on the west side of the reservoir where wind-driven currents upwell nutrients. The degree of oxygenation decreased with month and depth, increased from morning to afternoon and was higher on the east side where surface water is pushed by wind. -from Authors