Underwater wireless sensor networks (UWSNs) are becoming increasingly popular among researchers due to their potential for real-world applications such as marine surveillance, sea monitoring, deep sea archaeology, oil monitoring, and more. With almost 70% of the earth’s surface covered in water, it is challenging for humans to gather valuable information from the seabed without advanced technology. In UWSNs, sensor nodes are placed to sense the underwater environment, and the data collected is sent to a sink node, which then transfers the data to a base station for processing. The deployment of sensor nodes in UWSNs is difficult due to the harsh underwater environment, and the routing of data is complicated by the nodes’ limited communication range and high energy consumption. This study provides a comprehensive overview of UWSNs, including their applications, deployment methods, and routing algorithms. A comparative analysis of deployment techniques and routing algorithms is presented to help researchers identify research gaps in these areas. The study also reviews some UWSN applications, which offer valuable insights into the approach. The study covers the conventional technologies used in UWSNs and highlights significant research approaches towards UWSNs’ applications, deployment techniques, and routing processes. The insights provided in this study will assist researchers in understanding the present state of UWSNs and identifying future research directions in this exciting field.