Sources of anthropogenic (human-caused) underwater noise have increased significantly over the past fifty years, largely as a result of increases in seismic exploration, military and commercial sonars, and maritime transportation. Commercial shipping is one of the main contributors to anthropogenic noise and is mainly generated by propeller cavitation and onboard machinery. The low-frequency sounds that ships generate propagate efficiently and travel vast distances in deep water marine environments. This has sparked concerns about the impacts of underwater noise on marine life, which use sound to communicate, navigate, feed and reproduce. As the agency responsible for regulating shipping in Canada, Transport Canada considered it essential to better understand the problem of underwater noise within Canadian waters. This report assembles some of the technical knowledge about anthropogenic underwater noise and its potential impacts in a marine environment. It details information about how, based on the current satte of knowledge, the maritime industry contributes to ambient underwater noise and should facilitate understanding on how noise can pose a threat to the conservation of marine animals and to the recovery of species at risk.