The structures and stabilities of water clusters (H2O)(n) with 11less than or equal tonless than or equal to13 are determined by a genetic algorithm approach with two new evolutionary operators-namely annihilator and history operators. These studies show that the modified genetic algorithm provides an efficient procedure for calculating global minima with an especial attention to molecular water clusters. The actual results are in quantitative agreement with previous calculations using the basin hopping Monte Carlo method.