In order to avoid failure in its lifetime, a breakwater system has to be inspected and, if necessary, has to be repaired. In this paper, a comprehensive maintenance strategy with optimal inspection planning is formulated. Rational maintenance decision-making approaches are discussed. The proposed maintenance strategy combines time-dependent and condition-dependent maintenance with event-dependent inspection. Optimal inspection planning is obtained by cost optimization with a safety constraint. In practical cases, it is possible to achieve an optimal inspection plan when relevant parameters of strength and load are existing and available.