Water quality is the major limiting factor in the productivity of aquatic ecosystems, including fish resources. The objective of the study was to evaluate the water quality of Lake Hawassa. The water samples were collected from January to December 2021 from six sampling sites. The results indicated that the level of physico-chemical parameters such as pH (8.35-9.70), DO(4.36-6.20 mg/l), turbidity (9.40-29.62 NTUs), EC (600-960 ?S/cm), TDS (491.25-940 mg/l), BOD5 (100-165.93 mg/l), NH4+ (0.03-0.59 mg/l), NO3 – (2.80-7.00 mg/l) and PO4+2 (1-1.90 mg/l) exceeded the permissible limits for freshwater fish survival. The result also showed that total bacteria count, total coliform and faecal coliform count of the lake ranged from 1.80 x 105-5.80 x 105 CFU/ml, 0.50 x 104-3.50 x 104 MPN/100ml and 0.00-2.34 x 102 MPN/100ml, respectively. In addition, bacteria loads had significant and positive to negative correlation with physic-chemical parameters of the lake. There should be continuous monitoring of the lake by the relevant constituted authority to detect any changes in the water quality.

Keywords: Bacterial loads, lake ecosystems, pollution, water quality