Abstract:
Lake Hawassa is one of the Major Ethiopian Rift Valley Lakes which has endorheic1
basin
system and Hawassa Town established near to the Lake. The lake gave major recreational site for
the town and nearby cities. It receives inflow from the only perennial River Tikurwuha and
runoff from the remaining sub-catchment. Lake water quality is vital for the surrounding
community for proper and safe use of the Lake. The surrounding community uses the water for
multipurpose use, like irrigation, water supply, recreation and fish harvesting. The present study
was designed to examine the physicochemical and biological water quality suitability for
determine trophic state of the lake for a period of three months from June to August in the case
of summer or rainy time, 2017/18. Water samples were collected from the lake on monthly basis
and analyzed for all water quality parameters by standard methods. Data analysis was performed
by spreadsheet. The overall water quality parameters analytical results have been observed as pH
(8.9±0.12), TDS (422.2±21.43), Temp. (20.8±0.35), DO (5.2±0.26), Turbidity (6.6±0.1NTU),
COD (173.6±45.2), BOD5 (45±5.3), NO3ˉ (6.25), PO4
3-
(1.35±0.54), EC(812.8±21.5µS/cm), TA
(332.818), Clˉ (31.5±2.9), Chll-a(1037.018µg/l), Secchi depth (0.934) and units are mg/l except
specified. On average, the trophic state of the Lake Hawassa was under hypereutrophic stage as
per the standard depending on the value of Secchi depth, chlorophyll a, phosphate, and nitrate
amount. The current study showed the lake is unfit for any purpose as per WQI range. Since the
analysis undertaken during summer time, the rain water may reduce the amount of contamination
range of pollutant and it absolutely increases in winter time. There are a lot of problems seen on
the lake like eutrophication around the lake shore, on the other side three of the sample site like
referral hospital, Fiker recreational area, and Tikurwuha seen more contamination and minimum
amount of dissolved oxygen. According to the result of physicochemical and biological
parameter of the lake the lake needs to mitigation to control eutrophication. This study put some
remedial measure to control expanded eutrophication by managing point and non-point source of
wastewater generated from Hawassa town and agricultural area.
