Underwater logging is the process of logging trees from underwater forests. When artificial reservoirs and dams are built, large areas of forest are often inundated; although the trees die, the wood is often preserved. The trees can then be felled using special underwater machinery and floated up to the surface. One such machine is the sawfish harvester. There is an ongoing debate to determine whether or not underwater logging is a sustainable practice and if it is more environmentally sustainable than traditional logging. Underwater logging has been introduced in select locations around the world, including Ghana's Lake Volta, the largest reservoir by surface area in the world. A related form of logging consists of salvaging logs which loggers have abandoned after they became waterlogged and sank. This activity can be quite profitable, since the prime "targets" are decades-old trees of a size and species difficult or impossible to find in their natural habitat. History In the 1950s, the United States recognized that, during colonial times, loggers used to float felled trees over the Great Lakes and Maine rivers for transportation to mills. Logs that weigh over 62.4 pounds per cubic foot, however, would sink, and the loggers did not take the time to recover them. These logs are not completely lost, though, as underwater logs are safe from wood-decaying fungi that require wood, moisture, air, and temperatures estimated around 75 to 90 degrees. Underwater logs are also safe from stains. Cumulatively, many logs were lost over time, and International Undersea Services began log salvage operations on the Penobscot River in Maine in 1955. John Cayford and Ronald Scott researched in their book, Underwater Logging, where new prospects for underwater logging operations could take place in the United States. This came to be known as salvage logging. These processes have become more popular as relevant strategies and technologies progress, making underwater logging a viable means to recover lost resources. The underwater logging industry as a whole has diversified as technologies have allowed for new processes to arise and develop. Salvage logging, for example, recovers full-sized logs that were lost during past logging expeditions. Underwater logging itself, on the other hand, has developed to the point where new technology has allowed for the capability to cut down drowned trees that have been lost due to rising water levels. It is estimated that, "Buried in the water of reservoirs around the world are