Water resources, in time, place, and quantity, are often poorly matched to the needs of humanity. This disparity tends to be more accentuated in arid and semiarid regions, predominant in Iran. Reservoir systems are a common means to control and manage water resources. Due to limited resources and the increasing demands for water, these systems must be optimally operated to maximize the efficiency of water use. Evolutionary optimization algorithms provide reliable and simple methods for solving complex optimization problems. One of those methods, the water cycle algorithm (WCA), is used in this paper to find optimal operation strategies for the Karon-4 reservoir and a four-reservoir system in Iran. The results demonstrate the high efficiency and reliability of the WCA in solving reservoir operation problems.