An underwater wireless sensor network (UWSN) consists of numerous sensor nodes deployed below the water to monitor physical and environmental changes. But to locate the deployed sensor nodes is an issue. Global positioning system (GPS) doesn’t work below the water because of water depth and dense medium. Also manual and stable configuration of sensor nodes is not possible in case of UWSN due to water drift of 3 m/s. This gives the challenge of locating the sensor node to fetch data from that node. So, localization plays a vital role in many applications wherein the absence of GPS and manual configuration. Various localization schemes widespread motivation for the purpose of data tagging, node tracking and target detection. Here we are classifying various localization methods by which we can deploy various sensors under the deep sea water. Here, the authors have also compared some existing UWSN techniques with the help of network simulator to guide the research fraternity.