The Internet of Underwater Things (IoUT) is on the way. The key application areas of IoUT include ocean engineering, maritime security and environmental monitoring. To achieve interoperability between different underwater communicating systems and/or to ensure connectivity from the air to underwater (and reversely), an Internet Protocol (IP) adaptation layer is necessary. In this paper, we propose Underwater-SCHC (U-SCHC) based on the Static Context Header Compression protocol (SCHC), a standard at the Internet Engineering Task Force (IETF) for terrestrial Internet of Things. The purpose of the paper is to describe the protocol encapsulation in the context of very low bit rates and small payloads as are usually observed in underwater acoustic systems. As a result, we reach the header compression ratio of 99.74% with just a single bit allocated to the UDP/IPv6 stack.