Risk based design of hydraulic structures requires that the performance of these structures in accomplishing their intended purpose is assessed and improved if seemed necessary. Such an approach is not very common in Turkey so that the operational performance of most structures is overlooked and is not described in tangible terms. The presented study is realized upon this deficiency in the Turkish engineering practices and is expected to be one of the first studies to assess the performance of water structures in computable figures. The Author examined all methods for performance assessment of dam reservoirs and employed performance indicator method. He also explained all calculating details for more clear understanding, he hope that this study will be a major step in relevant engineering studies especially in Turkey.