Abstract In this paper, we exploit cooperative communication for design- ing an energy efficient routing algorithm in Underwater Wireless Sensor Net- works (UWSNs). Each network node is equipped with a single omnidirectional antenna and multiple nodes coordinate while taking advantage of spatial di- versity. This research work is limited in scope to Amplify-and-Forward (AF) scheme at the relay node and Fixed Ratio Combining (FRC) strategy at the receiver node. Cooperative diversity at the physical layer and multi-hop rout- ing at the network layer enable us to formulate minimum energy routing as a joint optimization of the transmission power at physical layer and link selection at the network layer. Simulations results show that our proposed Cooperative Energy Efficient routing for UWSNs (Co-EEUWSN) performs better than the selected non-cooperative routing protocols (Depth-Based Routing (DBR) and Energy-Efficient DBR (EEDBR)) and Cooperative DBR (Co-DBR) in terms of packet delivery ratio, end-to-end delay, and energy efficiency.