Changes to fluvial systems including flow regulation, dam construction, water diversion, land-use practices, and flood alteration establish new geomorphic conditions that affect aquatic ecosystem and its nature which was perfect by itself. Alluvial rivers adjust their geometry as a reaction for anthropogenic disturbances. This paper examines channel adjustment along a 35-km stretch of the Abay River which originates from Lake Tana and drains towards 45 m gorge at Tiss isat fall. Over 35 year‟s period, the natural outlet system of the river was disturbed. Sedimentation, change of hydrological regime and vegetation encroachment has become more frequent in recent times at the channel. The objectives of this study were to document the changes in channel planform and the hydro –morphological effect of Lake Tana level regulation by Chara Chara weir for hydropower production on the Abay River system from the source to Tiss-Issat fall. The characterization of the river discharge regime at the gauging station is based on the hydrographs, using the mean monthly time-series of measured discharge by four scenarios that is covering the period 1959-1995, 1996-2001, 2001-2010 and 2010-2020. Channel planform information was extracted from high resolution satellite images of Google Earth by mapping the active river bed for the years 1985, 2005 and 2020 and super imposing using Arc GIS10.3. The results indicate that operation of the Chara-Chara weir has altered the flow regime of the Abay River. Since 2001, the regulation has significantly increased dry season, and significantly decreased wet season, flows due to full regulation of Charachara weir. But Since 2010, both wet and dry season flows were significantly lower than those which occurred during the previous three periods as a consequence of diversions to the Tana Beles power stations. Bars and islands become expanded and vegetation encroach the channel due to loss of peak flood and reduction of active river bed. In general, this study showed that changes to the planform at the out let of the river and to the riverbed level are significant. Moreover, the study indicates that the active channel of Abay River loss is progressive and aquatic lives are disturbed in recent times. Upland watershed conservation is better to increase the natural base flow of the river. And also measures should be taken to return the feature of the Abay River waterway even if the encroachment of riparian vegetation is better for the habitat of birds and source of fire wood for local peoples.