Artificial lakes created by dams are used to store water for irrigation, water supply, recreation and other purpose. The construction of dam for water storage changes dramatically the hydrodynamics of the river with direct consequences on the river morphology, habitat and ecology of the whole river system. One major change with direct consequences on the river system is the formation of sediment storage at the head of the reservoir to form delta and back xiii water deposition. Suspended sediments are further transported by currents density through the old river channel in reaching at the end of the dam section and even some may pass through the bottom outlets. The amount of sediment deposit and distribution pattern could be estimated quantitatively by using bathymetric survey. Reservoir sedimentation is a very complex process by its nature .Sedimentation is a critical problem that undermines the useful life of reservoirs. Consequently, too urgent and relevant management interventions are required to reduce the accelerated loss of the water storage capacity of the reservoirs. For appropriate management plan information on current topographic conditions and any changes in the storage capacities of reservoirs are required. This study is the first in Tebi reservoir located in Amhara region, north eastern part of Ethiopia to quantify the amount of sediment deposition in the reservoir from 1999 to 2017 and to estimate useful life of the reservoir. Bathymetry survey and land survey were done to determine current capacity of reservoir below normal pool level. To quantify sediment deposition, comparison of reservoir capacity on two periods of time was applied by developing TIN and analyzing volume using Arc.GIS 10.2.2. The result showed that Tebi reservoir has lost 31.87% of its capacity due to sedimentation in 18 years (1999 to 2017). Average rate of sedimentation is estimated to be 22669.44 m3/ year giving 1.77% annual rate of loss. This is found to be greater than globally estimated annual rate of siltation of reservoirs (1.21%). Also the study indicated that reservoir capacity at intake level is reduced by 86.054% of its capacity at this level. Consequently useful life of reservoir is estimated to be remain 11 years. whereas reservoir life when 90 percent of the original capacity is filled up by silt remain 11 years . As a result Jerjero, Warle, Anjawa and Dabat Micro watersheds are prioritized as the first, second, third and fourth for planning and implementing conservation measures at Tebi reservoir watershed to minimize reservoir sediment deposition rate. Key words; Reservoir sedimentation, bathymetry, Tebi Reservoir