In this paper, we tackle one fundamental problem in underwater sensor networks (UASNs), routing. Aiming at many challenges to the routing protocol design of UASNs, which are bought by the features of UASNs, such as low bandwidth, high latency, dynamics topology resulted by node float mobility, high error probability and so on, a novel reactive routing protocol is proposed, called information-carrying based routing protocol (ICRP), to provide energy efficient, real-time and scalable routing. Because the control packet of establishing path is carried by the data packet, the information-carrying mechanism not only is energy efficient, but also results in low end-to-end delivery delay. It does not depend one the location information of nodes. No state information is required on the sensor nodes and only a small fraction of the nodes are involved in routing. Hence, the protocol is also scalable and is suitable stationary, mobile and hybrid network. We evaluate the performance of ICRP through extensive simulations and physical experiments. Our results show that ICRP can effectively achieve the goals of energy efficiency and low data delivery delay.