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In underwater wireless sensor networks (UWSNs), the sensor nodes are sparsely deployed over a large sea area due to their high design cost and high manufacturing cost. Opportunistic routing protocols are a promising forwarding technique for various UWSNs. However, many opportunistic routing protocols suffer from the void problem in sparse underwater scenarios. Hop count-based opportunistic routing protocols inherently alleviate this problem by periodically maintaining the topological information of sensor node. Nevertheless, the robustness of these protocols degrades due to channel variation and node movement in UWSNs. In this paper, we propose a coding-aware opportunistic routing method for sparse UWSNs (CORS). In CORS, we use topological information to adaptively expand the candidate set. On this basis, a forwarding with opportunistic coding strategy is developed to join interflow network coding and opportunistic forwarding in CORS. In addition, we design a sliding window-based coding algorithm to provide effective coding gains with low coding overhead. Then, a sliding window-based decoding algorithm is designed to reduce decoding overhead. Simulation results show that CORS significantly improves upon the network performances of existing protocols in various scenarios.