Ensuring adequate water supply for irrigation is crucial for enhancing the output of agricultural products. Irrigation water losses primarily result from seepage in canal base sections, evaporation, and operational inefficiencies. The present study aimed to assess the water loss or effectiveness of the irrigation channels of the Batu Bulan Dam, Sumbawa, Indonesia. The incoming and outgoing water discharge in the channel was examined. The extent of water loss in each irrigation channel was assessed by measuring the discharge and analyzing the estimates of channel discharge based on the velocity of water in the channel. The discharge in both the upstream and downstream channels was analyzed to assess the efficiency of the irrigation channel and identify potential strategies for minimizing water loss. The research findings indicate that principal channels constructed with stone masonry exhibit low efficiency due to significant water loss. While primary channels utilizing stone masonry are theoretically expected to have equal efficiency, in practice, secondary channels exhibit less efficiency. The occurrence of this outcome can be attributed to channel degradation in multiple areas. The accumulation of silt, in the form of dirt and weeds, around the primary channels diminishes the effectiveness of the channels. To enhance the efficacy of the Batu Bulan Dam irrigation channels, modifying the channel type and minimizing water wastage along the channels is imperative.