In Ethiopia the water resource in most lakes is decline and disappears. Due to this it needs accurate and detail study on the causes of reduction and mitigation measures of water resource. The objective of this study is to assess the impact of irrigation water use on the water level of Lake Hayq. The methodology was applying a continuity equation of water balance methods and CROPWAT 8.0 model to estimate the gross irrigation water requirements of six major crops irrigated in the study area. The annual water balance of Lake Hayq was determined from inflow components (direct rainfall over the lake and runoff from the watershed area) and outflow components (evaporation and water abstraction from the lake) for three different years (2002, 2010 and 2018). Average rainfall over Lake Surface was estimated using IDW interpolation method from long term recoreded rainfall data of Hayq, Dessie, Kombolcha and Wuchale; and surface runoff from the watershed were estimated from the lake level data using water balance equation. Evaporation loss from Lake Hayq was estimated by Penman method. The water abstraction for irrigation from the lake was estimated from both existing irrigated and future potential irrigable land. Water abstraction for the purpose of domestic use was estimated from human and animal population data based on daily water demand criteria. The total mean annual depth of inflow from rainfall and surface runoff into the Lake was estimated 49.2 MCM, 47.3 MCM and 44.4 MCM, and outflow from the Lake dueto evaporation and abstraction was estimated about 38.6 MCM, 41.1 MCM and 41.5 MCM in 2002, 2010 and 2018 respectively. Evaporation from the lake was the main component which affects the Lake Hayq water balance which covers about 41% of the total water balance of the lake and 1.5 times the areal rainfall of Lake Hayq. Water extraction for irrigation use was the second main water losses that affects the water level of Lake Hayq and it covers 0.03%, 0.19% and 0.24% of the volume of Lake Hayq in 2002, 2010 and 2018 respectively. The result of water balance of the lake Hayq shows that, the residual water balanceccomponents (the sum of groundwater inflow, outflow and change in storage was 10.6 MCM, 6.2MCM and 3.0 MCM in 2002, 2010 and 2018 respectively. Keywords: Lake Hayq, Irrigation Water use, Water level, water balance