Underwater wireless sensor network (UWSN) is a new technolog that can be used for various purposes, including ocean tracking and underwater exploration, military surveillance, disaster management, industrial applications, and scientific research. These applications require the sensed data to be routed to the destination, and this results in making the data routing one of the essential parts in designing such applications. High propagation delay, restricted bandwidth, 3D deployment, and energy constraints are some of the challenges that UWSN faces when developing routing protocols. Therefore, to mitigate these challenges, efficient routing protocols are proposed according to the specific application. This paper surveys recently routing protocols for UWSN. Furthermore, each routing protocol's main idea and essential operation are presented and its merits and demerits. There are two types of routing protocols …