Abstract: The paper presents an acoustic system for the transmission of digital data in shallow coastal waters of which multi-path propagation and intense reverberations are characteristic. To ensure a small error probability of moderate speed transmission, the system uses corrective codes and a technique of incoherent modulation MFSK (Mufti Frequency Shift Keying). To synthesise the transmission signal, estimate the spectrum of the signal received and code and decode the channels, a DSP processor was used. The paper includes the results oj a computer simulation in which the system was put to work in the presence of Gaussian noise. The system was tested in shallow coastal waters and the results are discussed in the paper.