Water is an excellent medium for sound transmission and many aquatic animals actively produce sound for communication, orientation or foraging purposes. The underwater environment is filled with abiotic and biotic sounds of variable intensity over a wide range of frequencies and showing high levels of variation in space and time. Evidence is increasing that the passive use of such environmental sounds also provides an important information source for aquatic organisms to orient themselves and obtain information about the environment. All fishes can detect and process acoustic particle motion, including species that do not produce sound, indicating that sound is likely to be of critical importance in the lives of many fish species. Over the last century, human activities in and near the water have increasingly added artificial sounds to the underwater environment. To date, information on the behavioral and ecological implications of increasing underwater sound levels for fish is generally lacking. However, comparative evidence from other vertebrate species suggests that impeding the ability of fish to hear biologically relevant sounds can interfere with critical functions such as acoustic communication, predator avoidance and use of information from underwater soundscapes. Sounds produced by offshore windpower plants comprise loud impulse sounds (construction) and more moderate underwater noises of longer duration (operation and maintenance), which differ substantially in the type of impact and the spatio-temporal scale over which effects may occur. Short impact sounds, such as from pile driving can have dramatic effects on nearby fish, resulting in physical damage and death. However, long-term moderate anthropogenic noise exposure may have a greater impact on fish behaviour and ecology, potentially affecting whole ecosystems. Before noise-exposure criteria and mitigation measures can be established for fish, experimental studies in the field and in the laboratory are needed to investigate if and how fish are impacted behaviorally and physiologically by chronic and impact noise. Comparative evidence from terrestrial studies may provide guidance in experimental design and in taking a more holistic approach to develop a better understanding of the ecological impact of anthropogenic noise.