A pilot study on anthropogenic faucal pollution impact in Bahir Dar Gulf of Lake Tana, northern Ethiopia

The anthropogenic effect on faecal and chemical pollution at Bahir Dar Gulf of Lake Tana, Ethiopia was investigated in the period of October 2006 to February 2007. Faecal and physicochemical pollution levels were signifcantly increased and clearly discernible in the Bahir Dar Gulf locations as compared to presumptively anthropogenic uninfuenced reference locations near the outlet of the Blue Nile River of Lake Tana. One directly sewage infuenced lake site at Bahir Dar Gulf was found to be excessively faecally polluted. The total pooled data set from the study for faecal coliforms, Escherichia coli and Clostridium perfringens spores ranged from not detectable (n.d.) to log 6.2 CFU, n.d. to log 6.1 CFU and n.d. to log 1.7 CFU per 100 ml, respectively. A high variation was also observable for the physicochemical parameters including the spectral absorption coeffcient at 254 nm, ammonia, nitrite, nitrate, total dissolved solids, total suspended solids and pH values. Although the data have to be considered preliminary, it strongly points to the need for systematic water quality monitoring of Lake Tana and its potential impact sources. This is all the more important as the lake is the largest freshwater body in the country serving a multipurpose role and being identifed as a growth corridor of the country.