Network efficiency and reliability in terms of high throughput, energy conservation, low bit error rate (BER) and reduced delay are pre-requisites for many applications in Underwater Wireless Sensor Networks (UWSNs). However, distinctive features of UWSNs like low available bandwidth, large propagation delay, highly dynamic network topology, and high error probability pose many challenges for devising efficient and reliable communication protocols. In this paper, we therefore propose a protocol that focuses on enhancing network reliability and efficiency using cooperative routing and sink mobility. Many cooperative communication protocols have been developed which investigate the physical and MAC layer aspects to improve link efficiency in harsh underwater environment, however, at network layer, it is still unexplored. Similarly, cooperative routing is not yet collaborated with sink mobility. In this paper, Cooperative routing is implemented at network layer along with sink mobility. Potential relay and destination nodes for cooperative routing are selected on the basis of their depth as well as residual energy information. Data from source node is forwarded towards the destination node via relay nodes in a cooperative manner. Sink mobility further improves the results by directly gathering data from nodes. Based on the comprehensive simulations imple-mented in MATLAB, we observe that our scheme improves the performance in terms of network lifetime, energy efficiency and throughput along with reducing delay and BER. I. RELATED WORK Taking advantage of the broadcast nature of wireless transmission, cooperative communication has been proposed as a powerful alternative to reduce fading and other link impairments, where transmitted signal can be overheard by many unintended sensor nodes , . Some related work presented in this domain is presented here An innovative physical layer solution involving cooperative communication is given in , where outage probability and capacity expressions are derived for cooperative multicarrier UAC systems with AF and DF relaying. Further, they pro-pose a receiver design to mitigate the degrading Doppler effects. In , Cooperative UnderWater Acoustic Multiple Input Single Output (CUWA-MISO) using DF is proposed where each node of network uses nearest adjacent node as a virtual antenna in a cooperative manner. It improves the system performance with the help of spatial diversity. Luo et al. , explored cooperation at MAC layer and proposed a distributed MAC protocol, that is, Coordinated Transmission MAC (CT-MAC) for underwater MIMO based network uplink communication. The scheme also addresses long propagation delay and collision among control packets in UAC. Authors in  suggested that channel efficiency is improved by applying asynchronous cooperative transmission for three dimensional UWSNs. Two typical forwarding schemes: AF and DF are implemented, analyzed and compared. In COoperative Best Relay Assessment (COBRA) , a relay selection criterion for underwater cooperative acoustic networks is developed. COBRA minimizes the One-way Packet Transmission (OPT) time. The best relay selection algorithm is used here. In , authors consider cooperative scheme with a design aspect from the physical layer to the network layer, leading to the efficient operation and reduced transceiver's complexity. It enhances the reliability by providing diversity gains through intermediate relay nodes.