An underwater acoustic communication scheme using intrinsic dolphin sounds is proposed to overcome the sound exposure derived from traditional fixed carrier modulation for covert communication in this paper. The communication signal can be detected but it could easily be excluded in the process of recognition/classification by an adversary. This is because the signal resembles dolphin sounds. Properties of dolphin sounds are investigated in this paper. Synchronization in this scheme is achieved by using dolphin whistles while dolphin clicks are used as information carrier. The time interval between dolphin clicks conveys information. Channel equalization is performed by passive time reversal mirror technique, whereas channel estimation is done through matching pursuit method under the theory of compressive sensing. The efficiency and feasibility of the proposed method are verified by lake trial. The received signal and emission mimic bio-signal are very similar. Bit error rate less than 10-4 is achieved above 29 bps to a distance of about 2 km.