Sonar: the sound source that is the subject of this article.
Motorised shipping.
Seismic surveys, in which 'airguns' are used to fire into the seabed to map gas and oil fields.
Pile-driving work, for example for the construction of offshore wind farms.
Explosions, usually to dispose of a mine, torpedo, or bomb found on the seabed, or sometimes for fishing using explosives.
In many cases of underwater noise, efforts are being made to reduce noise pollution in the natural world. When pile-driving, bubble screens – a kind of curtain of bubbles – can shield the surrounding area from the noise, and when a bomb is to be detonated, animals are quietly chased away from the area beforehand to protect them from the potentially lethal pressure wave from the blast.