Time Saving and energy consumption has become a vital issue that attracts the attention of researchers in Underwater Wireless Sensor Networks (UWSNs) fields. According to that, there is a strong need to improve MAC protocols performance in UWSNs, particularly enhancing the effectiveness of ALOHA Protocol. In this paper, a time-saving Aloha protocol with slotted carrier sense proposed which we called, ST-Slotted-CS-ALOHA protocol. The results of the simulation demonstrate that our proposed protocol can save time and decrease the average delay when it compared with the other protocols. Moreover, it decreased energy consumption and raised the ratio of throughput. However, the number of dropped nodes does not give better results compared to other protocols.