Water covers over 70% of the globe, yet our ability to communicate in the underwater environment is limited. Radio and light communication through water suffer from such major issues that acoustic waves are the dominant form of cable-free underwater communication, but themselves suffer from low bandwidth and poor signal quality. Absorption on hydro-acoustic communication channels grows rapidly as frequency rises. Hence most contemporary hydro-acoustic communication takes place at relatively low carrier frequencies, limiting the signal bandwidth. Communication at high-frequencies is only possible over short link distances. In this work we highlight that networks support long-range communication by providing a backhaul, and that the energy savings from a multi-hop relaying strategy can make communication in a high-absorption medium operate at similar energy costs per bit metre to those of longer range single hop communications in an absorption-free medium. Effectively a relaying strategy can mitigate the effect of a high absorption rate. All networks, especially multi-hop networks suffer from congestion. We show that provided the absorption rate can be selected, interference in a network can be managed effectively by absorption, even as the node spacing shrinks without bound. Energy savings from a multi-hop strategy allow realistic access to high operating frequencies, with corresponding large bandwidths, and the high absorption rate ensures adequate isolation between nodes, alleviating congestion. In the context of multi-hop networks we show that there is an absorption rate that maximises the network transport capacity. This is useful because in a hydro-acoustic network the absorption rate is a strong, but well behaved, function of frequency. Hence in such networks, absorption is selectable by the choice of operating frequency. With absorption selected for optimal transport capacity, we find that the network transport capacity, normalised for area and bandwidth, is proportional to the absorption rate. This provides a shortcut to determine the available Network Transport Capacity in any network when the absorption rate - or the hydro-acoustic frequency - is known. Finally we conduct a practical test to advance the technology which could be used to build high-frequency hydro-acoustic networks that utilise absorption to enhance spatial reuse of the common channel.