Underwater sensor networks (UWSNs) are becoming popular everyday due to their ability which makes them to be deployed under adverse environmental conditions. UWNs are the enabling technology for wide range of applications like pollution monitoring, nutrient production, oil retrieval and transportation. The use of acoustic communication underwater environment posses many interesting challenges. Because of high transmission power, energy consumption is more, making medium access protocol a primary focus point for reducing energy consumption. However sensed data can be interpreted meaningfully when referenced to the location of the sensor, making localization an important problem. In this paper, we give a survey on the architectural view and protocols used for underwater sensor networks.