The whole globe is covered universally by water with a majority space. In view of extraction of minerals as well as national security reasons, underwater communication has become quite important for all the mankind. Researchers, around the world are working for optimizing the multiple scheme in acoustic channel. Recently, the researchers have reported valuable employability of IDMA scheme in acoustic communication. In IDMA Scheme, the users are distinguished with userspecific interleaving sequences based on chip-level interleaving mechanism instead of user-specific signature sequences as engaged in CDMA scheme. However the role regarding formation of interleavers plays vital notch for performance of IDMA scheme in underwater communication. In this paper, the performance of user-specific rotational interleaver has been observed in acoustic environment for BPSK signaling scheme on MATLAB platform. Simulation results demonstrate that the rotational interleaver performs better in terms of bit error rate (BER) for underwater channel employing iterative IDMA system.