One approach for ocean-bottom and column monitoring is to use oceanographic sensors, record the data, and recover the instruments. This approach creates long lags in receiving the recorded information. In addition, if a breakdown occurs before recovery, all the data is lost. An appropriate solution for these applications is to design an underwater acoustic network (UWA) in order to establish real-time communication between the underwater instruments. However, underwater networking has several challenges. While many underwater applications require long-term monitoring of the deployment area, the battery-powered network nodes limit the lifetime of UWA networks. On the other hand, underwater acoustic channel characterized by low available bandwidth, highly varying multi-path, and large propagation delays. In addition, the path loss in underwater acoustic communication channels depends not only on the distance between the transmitter and receiver, as it is the case in many other wireless channels, but also on the signal frequency significantly. Within such an environment, designing an UWA network that maximizes throughput and reliability, while minimizing the power consumption, becomes a very difficult task. One of the questions that arise naturally at this time is that if two transmitters that their relevant receivers are in the vicinity of each other, send their data at the same time, the Signal to Interference ratio (SIR) decreases at the receivers. Hence, what are the fundamental capabilities of underwater networks in supporting multiple nodes that wish to communicate to (or through) each other over an acoustic channel in order to satisfy the QoS requirements? While research has been extremely active on assessing the capacity of wireless radio networks, no similar analyses have been reported for underwater acoustic networks.