As over 70 percent of the earth’s surface is covered by water, it is desirable to deploy underwater sensor networks to support oceanic research. Under Water Sensor Networks (UWSNs) use acoustic waves and are characterized by long and variable propagation delays, intermittent connectivity, limited bandwidth and low bit rates. Energy savings have always been the primary concern in wireless sensor network protocols; however there are applications where latency and throughput are prioritized over energy efficiency and are so significant that the application would not be able to satisfy its requirements without them. Although existing duty-cycle MAC protocols are power efficient, they introduce significant end-to-end delivery latency, provide poor throughput and are not suitable for the challenging environment of an UWSN. In this paper, we utilize CDMA as the underlying multiple access technique, due to its resilience to multi-path and Doppler’s effects prevalent in underwater environments. We propose UWMAC, a CDMA-based power controlled medium access protocol that uses both transmitter based and receiver based CDMA inside a formed cluster, and uses a TDMA schedule to make the cluster heads communicate with the base station. Our MAC algorithm targets latency and throughput needs in addition to its ability to increase the overall network lifetime. We discuss the design of UW-MAC, and provide a head-to-head comparison with other protocols through extensive simulations focusing on the performance in terms of latency, throughput and energy consumption.