Underwater acoustic sensor networks are characterized by limited transmit power and bandwidth, and a harsh communication environment. Different techniques for reliable communication in underwater networks have been studied in the literature at different layers of the network protocol stack. Among these, the use of fountain codes as a way for improving the quality of the communication over a highly impaired channel has been proposed. However, additional power consumption at both the transmitter and receiver are introduced by the coding and decoding complexity. In this paper, we propose a novel energy-aware adaptive protocol for data dissemination based on fountain codes. Our protocol exploits the intrinsic relationship between transmission/reception energy consumption and coding/decoding complexity introduced by fountain codes to dynamically adjust the encoding scheme in order to efficiently distribute the energy consumption of the communication and processing among the transmitter and the receiver. Simulation results show the benefits of our approach under different conditions.