A scheme for positioning swimmers using underwater acoustic networks is proposed. The design and the performance of such a network are presented. Owing to its high accuracy, the spherical interpolation approach is employed as the positioning algorithm. The configuration of the network, namely, the arrangement of anchor nodes in the swimming pool, is optimized to achieve the highest accuracy with the minimum number of nodes and therefore the lowest cost. The simulation study includes both two dimensional (2D) and three dimensional (3D) cases in order to understand the variation of positioning estimation accuracy in horizontal and vertical directions.