Improper water distribution and allocation lead to the presence of water scarcity, conflicts, management problems, and social challenges. Therefore, the objective of this study was assessing the irrigation water management issues in the Koga irrigation scheme. Koga irrigation scheme located in Mecha woredas having a total area of 7004 ha irrigated land and 11-night storage with 12 irrigation blocks were constructed in 2002. The total of 120 households was purposively selected at the head, middle and tail of the irrigation scheme. The required data were collected by interviewing about Koga irrigation management issues. The crop water requirements of the major irrigated crops were calculated by CROPWAT version 8 and the social data were analyzed by SPSS version 20 and the water balance was computed using excels. According to the water balance calculation result, the difference between water supply and water demand showed that irrigation water management was the dominant problem of the scheme. Water scarcity, conflict, distribution and allocation problems, weak participation, and management challenges were increased from the upper to the lower part of the command area. In Koga, 85.2% of irrigators were the dominant user of irrigation water at the head of the scheme. 11.1%, 63% and 74.1% of the respondents said that unfair water distribution and allocation were big problems at the head, mid and tail of scheme respectively. The role of irrigation users in the organizations at all scheme classes was generally very low according to farmers’ opinion. This perception of farmers on the participation of water user association (WUA) was highest at the lower users of the Koga irrigation scheme. The presence of conflict was 25.9%, 77.8% and 88.9 % at the upper, middle and lower class of the scheme respectively. This study found that the presence of conflict increased from the upper part of the irrigation scheme to the lower with the integration of water scarcity, water management problems and poor participation of farmers in water users and irrigation cooperatives.