In Depth Adaptive Routing Protocol (DARP)  authors considered the fact that speed of sound varies with depth and proposed shortest delay path for deep sea (about 8000 m) underwater environments. Relative Distance Based Forwarding (RDBF) is proposed in . In RDBF, fitness factor is normalized by transmission range to get the value in range of [0, 1]. Holding time is also dependent on transmission range and speed of sound in acoustic environment. Multi Path Routing (MPT) proposed in  ensures balance between energy consumption and end to end delay for time critical underwater applications. Its a cross layer approach which employs: (1) power control on physical layer according to channel status and network conditions; (2) packet combining mechanism on sink for multiple copies of corrupted packets received from different paths. MPT perform well in dense deployment scenarios while suffers void regions in sparse networks.