Net cage aquaculture has developed rapidly since mid 1980's in Turkish Coasts. Rapid and uncontrolled development had brought some environmental problems. Uneaten feeds and feaces effected water column and sediment in a negative way especially in closed and semi-enclosed bays. Together with the advances in net cage technology, offshore aquaculture which makes possible more intensive and efficient production has brought new trend to cage aquaculture. The aim of this study was to monitor probable impacts of the offshore aquaculture farm produced sea bream and sea bass on water column located in Ildir Bay. For this purpose, 8 seasonal samplings were carried out at three stations from surface and bottom waters on May 2000, July 2000, October 2000, February 2001 and February 2004, May 2004, August 2004, November 2004. Physico-chemical variables (temperature, salinity, pH; dissolved oxygen, Secchi depth) and nutrients (Nitrate, nitrite, ammonium, phosphate) of the samples were investigated. Measured values changed between; 14.0-24.5 degrees C for water temperature, 7.85-8.48 for pH, 33.97-41.00% for salinity, 5.2-9.2 mg/L for dissolved oxygen, 10.5-32.9 m for secchi depth, nd (non detected)-0.44 mu g at/L for nitrite, nd-1.12 mu gat/L for nitrate, nd-9.07 mu gat/L for ammonium, nd-0,61 mu gat/L for phosphate. In conclusion, significant changes were not detected in water quality because cages are situated offshore and consequently depths are high and feeding is carried out under control.