The advancement of the underwater Wireless Sensor Network (UWSNs) has drawn emerges consideration of numerous researchers from industry and scholars to sense and monitor the unexplored underwater area which is nearly 70% of the earth. Regardless of the striking impact of the sea on worldwide living life forms, it is viewed as that 95% of its ability stays obscure by natural eyes. This issue can be tackled by constant data recovery to people. Underwater communication is an emergent terminology for monitoring and discovery of underwater resources. This network enables for determining the uncovered sources like sank ships, Bermuda triangle trouble, oil mines, and plate tectonics within the water. The unearthing of those resources is tough due to the distant underwater obscure areas. This manuscript discusses the data fusion concept in UWSN with the help of related work. Further, the challenges of UWSNs data fusion are presented. Additionally, different existing data fusion methods are discussed through NS2 w.r.t. different QoS parameters like network lifetime, packet loss rate, energy consumption, delay, packet delivery ratio are considered in these simulations. Finally, the upcoming challenges and open issues during data fusion techniques are deliberated.