###### Abstract  
The underwater wireless sensor network (UWSN) is considered a promising technology for collecting valuable data from underwater areas, particularly for aiding military operations and environmental predictions. UWSNs consist of underwater sensor nodes that have limited energy and use acoustics for communication. Routing in underwater sensor nodes is one of the challenging issues in UWSNs because of the need to forward data packets with minimal energy consumption and a high packet delivery ratio. Selecting the next forwarding nodes is one of the key components of routing in UWSNs and has a direct effect on energy consumption and the packet delivery ratio. Therefore, this problem has gained much attention from the research community with the intent of enhancing the performance of UWSNs. This paper qualitatively reviews routing protocols for UWSNs, focusing on the next-hop selection method and its strengths and weaknesses. A taxonomy is presented for reviewing routing protocols under different categories of the classification. A summary of the qualitative investigation is presented highlighting aims, the next-hop selection method, metrics, and priority considerations. A comprehensive investigation is carried out focusing on energy, link quality, void awareness, reliability, and shortest path characteristics. Finally, we discuss potential future research directions in UWSNs for forwarding node selection. energy consumption; forwarding selection; routing; underwater wireless sensor network; void-aware +
Footnote †: journal: Information  
000.0  
Routing is one of the fundamental issues in UWSNs. Most of the studies on UWSNs concentrate on MAC and physical layers. Nevertheless, some studies have been conducted in the network layer; however, the study of this area is still in its initial stages [8; 9]. The process of designing and implementing a routing protocol for UWSNs is challenging due to the harsh underwater environment, characterized by high error rate, long propagation delay, low bandwidth, and energy limitations [10; 11; 12]. Therefore, this study takes into account these challenges and limitations in order to analyze the efficiency of routing protocols in UWSNs. The selection of the next forwarding nodes is one of the major decisions in the design of routing techniques for UWSNs and has a direct effect on the energy consumption and packet delivery ratio [4; 13; 14]. More precisely, the next forwarding nodes have been chosen based on the selected metrics. The best node forwards the data packets, and the rest of the nodes hold the data packets. The holding nodes forward the same data packets if the computed holding time finishes without overhearing the forwarding of the same data packets. Several forwarding nodes' selection algorithms have been suggested to reduce the energy consumption and increase the reliability in routing protocols for UWSNs [15; 16]. Therefore, the design and development of reliable energy-efficient routing techniques are still being investigated to reduce the energy consumption and improve the packet delivery ratio. In this context, this paper carries out a comprehensive review of routing algorithms for UWSNs, focusing on next-hop selection technology and challenging. The impact of the selection of next forwarding node on the assign of routing protocols in UWSNs is also highlighted. We categorize recent routing protocols for UWSNs based on the taxonomy presented for reviewing related literature. Under the categorization, we discuss each routing protocol, highlighting the next-hop node selection method and its strengths and weaknesses. We summarize and compare routing protocols for UWSNs based on the number of characteristics. The summary is based on different features including metrics, next-hop selection method, and priority for the best node. The comparison is based on the following performance factors: energy, link quality, void-aware, reliability, multi-hop, and shortest path.