Localization issue is a crucial part of Wireless Sensor Networks (WSNs) including Underwater WSNs (UWSNs). Unlike in Terrestrial WSNs where the localization techniques are well established, localization for UWSNs is still at the infancy stage. Most of the existing localizations proposed are based on Time of Arrival (ToA) and many of them assume an ideal environment and precise synchronization among sensor nodes. This research has proposed a new localization technique for UWSN based on Received Signal Strength Indication (RSSI)