Bahr Al-Najaf Depression Reservoir (BNDR) is located 5 kilometers south-southwest of Najaf city in central Iraq. It covers an area of approximately 360 square kilometers. Carlson’s Trophic State Index (CTSI) was applied to the BNDR. To do so, Chlorophyll (A), total phosphorus (TP), Secchi disc depth Transparency (SD) and some physiochemical parameters were measured. The mean value of Chl-a was 1,06 (±1,33), the maximum and minimum values of TSI based on total Chl-a were recorded during summer and spring respectively. The classification of trophic state using TSI (TP) and TSI (SD) was closed, but by using TSI (Chl-a) it was much higher, the value of TSI (Chl-a) > TSI (TP) >TSI (SD), the CTSI value of BNDR was between 35.11-71.33 (r2 = -27, 53), the highest value of CTSI was in summer while the lowest values were during winter, the average of physiochemical parameters (±standard deviation) were: 26,5 (±1,42), 7,6 (±0,88), 0,1 (±0,16), 71 (±16,57), 10100 (±5591), 1,55 (±2,26), 53350 (±24143), 243299 (±358773), 30752 (±44649), 20 (±13), 2499 (±1819), 2659 (±2561), 0,22 (±0,02), 0,32 (±0,06) for temperature, pH, DO, Ec, HCO- 3, TN, TH, Cl- SO= 4 , TOC, Na+, K+, Fe+, and Mn+ respectively. According to CTSI, BNDR can be classified as eutrophic. CTSI results were very close to those of lakes Sawa and Al-Razzazah, while there were some slight differences when compared with Al-Habbanayh and Derbandikhan lakes, where the level of trophic index was decreasing (56, and 52 for Al-Habbanayh lake and Derbandikhan lake respectively).
2016. Vol. 24, 1