## 1 Introduction  
Wireless sensor networks (WSN) have considerable potential in monitoring aquatic environments by sensing, collecting, and transferring data wirelessly to users in real time. It has indirectly led to the emergence of a new paradigm of wireless sensor technology known as underwater wireless sensor networks (UWSNs). UWSN technologies are implemented and deployed in deep underwater with sensors using acoustic signals to perform communication. Although UWSNs have exhibited a significant growth in the world market, a diverse range of application requirements have contributed to the pressing constraints on the performance of network tasks, and the capability of sensor nodes deployed in the monitored region. Furthermore, the available UWSN sensor nodes in the market have limited power and capacity, channel reliability, and complexity in acoustic signal communications [1, 2]. Therefore, the underwater wireless sensor network theories and applications are still required further exploration and review. Table 1 summarizes the existing recent relevant studies and highlights the research gap. However, these surveys covered only some basic features that still need to be updated based on the current research, technological advances, and new applications. From Table 1, it is conclude that many studies have failed to consider the crucial aspects in UWSNs. Hence, this study is conducted with the aim of investigating the domain of underwater wireless sensor networks and provide comprehensive insight into UWSNs requirements, platforms, recent advances, taxonomy and challenges of UWSNs. Additionally, this paper offers the newest evidence for various aspects that can satisfy the requirements for rapid development of UWSNs. The contributions of this paper are summarized as follows:  
* Present a brief compilation of motivation for UWSNs and its significance. * Identify and describe the key requirements to achieve essential procedures of implementing UWSNs. * Investigate and present required platforms for developing robust UWSNs applications. * Propose a thematic taxonomy to classify existing literature based on the most important parameters and comprehensively investigate recent advances solutions to get details concept and technical aspects. * Highlight open research challenges of UWSNs as a guideline for future research to drive innovative development in various fields. The paper is structured as follows: Section 2 briefly describes architecture and essential characteristics of underwater wireless sensor networks. Section 3 explains the research motivation and its significance for UWSNs. Section 4 discusses various platforms for developing UWSNs applications. Section 5 provides key requirements for implementing UWSNs. Section 6 compares, classifies and analyses the state-of-the-art of underwater wireless sensor networks with recent works. Section 7 details the research challenges in UWSNs. Finally, this paper concludes by summarising and emphasizing the future direction in Section 8. The paper is organized as illustrated in Figure 1. Abbreviations in this paper are defined in Table 2. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline \multirow{2}{*}{**Contributions**} & \multicolumn{5}{c}{**Previous Study**} & \multirow{2}{*}{**Proposed Study**} \\ \cline{2-2} \cline{4-6}  & [3] & [4] & [5] & [6] & [7] \\ \hline Underwater Sensor Networks Architecture & & & & & & \\ \hline Platforms for UWSNs & & & & & & \\ \hline Requirements of UWSNs & & & & & & \\ \hline Thematic Taxonomy of UWSNs & & & & & & \\ \hline Architectural Elements & & & & & & \\ \hline Underwater Acoustic Communications & & & & & & \\ \hline Routing Protocols & & & & & & \\ \hline Security & & & & & & \\ \hline Applications & & & & & & \\ \hline Open Research Challenges & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of the Proposed Paper with the Existing Surveys in UWSN.