In order to verify the feasibility and effectiveness of the whale optimization algorithm for reservoir optimal operation, four test functions were used in the whale optimization algorithm, and the simulated results were compared with those obtained from six algorithms, including the cuckoo search algorithm, differential evolution algorithm, shuffled frog leaping algorithm, particle swarm optimization algorithm, firefly algorithm, and SCE-UA algorithm. The whale optimization algorithm and the six comparison algorithms were used to solve the long-term optimal operation of a single reservoir and cascade reservoirs. The results show that the accuracy of the whale optimization algorithm is higher than that of the other six algorithms by eight or more orders of magnitude, and it has the fast convergence speed, high convergence precision, and excellent ability of optimization. The results of the whale optimization algorithm for the optimal operation of a single reservoir and cascade reservoirs are superior to those of the other six algorithms. The whale optimization algorithm is feasible and effective for reservoir optimal operation.