Comparative Assessment of the Water Quality Deterioration of Ethiopian Rift Lakes: The Case of Lakes Ziway and Hawassa Wondimu Tadiwos Hailesilassie 1* , Tenalem Ayenew Tegaye 2 1 Addis Ababa University, College of Natural and Computational Sciences, African Center of Excellence for Water Management, P.O. Box 1176, Addis Ababa, Ethiopia 2 Addis Ababa University, College of Natural and Computational Sciences, School of Earth Sciences, P.O. Box 1176, Addis Ababa, Ethiopia Corresponding Author Email: wonde721@gmail.com https://doi.org/10.18280/eesrj.060403 ABSTRACT Received: 19 September 2019 Accepted: 26 November 2019 The Ethiopian Rift Valley Lakes Basin consists of chain of lakes, many feeder streams and wetlands with unique hydrological and ecological characteristics having regional and global environmental importance. With growing population and consequent various human activities and degradation of watersheds aggravated by climatic change, the water quality of rivers and lakes and feeder rivers are deteriorating fast. The purpose of this study is to assess physico- chemical water quality parameters in two of relatively fresh water lakes (Ziway and Hawassa) which are occupying in the Central Main Ethiopian Rift floor. These parameters are pH, dissolved oxygen (DO), total dissolved solids (TDS), turbidity (NTU), Electrical conductivity (EC), and fluoride ion concentration(F - ). The mean values of those physico-chemical parameters were compared with maximum permissible limit (MPL) for drinking water as standardized by the Ethiopian Ministry of Health (MoH) and the World Health Organization (WHO). The result revealed that most of the parameters show clear deterioration over the last few decades. The likely factors are rapid urbanization, sedimentation, excessive use of fertilizers and industrialization in towns established along their shorelines. Hence, these trends demand immediate intervention to avert the grave environmental consequences. Keywords: environmental change Ethiopian rift, water quality, Hawassa, Ziway 1. INTRODUCTION Lakes and surface water reservoirs are considered as one of the planet’s most important freshwater resources and provide innumerable benefits. Lakes are stagnant surface water bodies, receive and stores rain fall water and from feeder streams and overland flow. The entire life of the world depends on water and therefore the hydrological study is very essential to comprehend the relationship among its diverse trophic levels and food webs [1]. Garn et al. [2] examined that lakes are subject to a variety of physical, chemical, and biological problems that can diminish their aesthetic beauty, recreational value, water quality, and habitat suitability. A study by Babu and Mohan [3] noted that the physio-chemical analysis is the prime consideration to assess the quality of water for its best utilization like drinking, irrigation, fisheries, and industrial purpose. Although the availability of different constituents in water has to be analyzed regularly to confirm its suitability for different purposes [4], the Ethiopian Rift Valley Lakes Basin consists of chain of lakes, streams and wetlands with unique hydrological and ecological characteristics. With an expansion of human activity, population, pressure, and a changing climate, water quality of lakes have been reported to be deteriorating in the recent past [5-8]. Lakes are surface waters which are vulnerable to pollution due to its easy accessibility for disposal of pollutants and wastewater [9]. Anthropogenic forces drive degradation of lake water quality in Ethiopia. Urbanization, industry, agriculture, and deforestation are the major anthropogenic drivers of many more specific processes [10-12]. As a result of lake degradation there are immediate impacts on human and natural health, as well as secondary or tertiary consequences as a result of decreased productivity and resource levels [13]. According to the Rift Valley Lakes Basin (RVLB) Master Plan Study Project which was carried out by the former Ethiopian Ministry of Water Resources (MoWR), the water quality analysis results for Ziway Lake in 2007 indicated that Lake Ziway was fresh and very good and can meet the quality requirements standards set for most of water uses such as drinking, irrigation, bathing and animal watering. The water is slightly alkaline and fresh [14], in addition to this, water quality of Lake Hawassa in the same year with the exception of the fluoride and pH value other quality parameters were within the WHO drinking water quality guideline values [14]. Recent studies on Lake Ziway showed that the lake is highly polluted due to various anthropogenic activities around the lake system, for instance, the recent studies showed that, there are intensive use of fertilizers for large- and small-scale irrigation practices in its watershed [8, 15]. Furthermore, floriculture development around Lake Ziway uses extremely high fertilizer. Large flower farms maintain a year-round production of cut-flowers and use the lake excessively [8]. The urban effluents from the city of Hawassa influenced Lake Hawassa significantly [11]. Other factors that influence Lake Hawassa include effluents of various factories like Hawassa Textile Factory, soft drink factory, ceramic factory and sewage Environmental and Earth Sciences Research Journal Vol. 6, No. 4, December, 2019, pp. 162-166 Journal homepage: http://iieta.org/journals/eesrj 162