The lack of scientifically based methods for assessing the need for forces and means complicates prompt decision-making in conditions of limited resources and highly dynamic situations when responding to incidents in the waters of megacities. The main results of this study include the development of a mathematical model for determining the required number of forces and means when conducting search and rescue operations in the waters of Saint-Petersburg. The model takes into account hydrometeorological conditions, the type of incident, the characteristics of rescue vessels and other factors. An algorithm for calculating the search area, the time of work and the optimal search strategy is proposed. A practical example shows how the model allows justifying the sufficiency or necessity of attracting additional forces. The practical significance lies in the possibility of introducing the model into an automated decision support system, which will reduce the time for assessing the situation, minimize the human factor and increase the efficiency of resource use during search and rescue operations.