Definitions of water pollution are mainly based on spills caused by human activity. They exclude natural seepage of hydrocarbons, eruptions on the seabed close to the coast, mudflow on the continental slope and inflow of sediment by flooding rivers. Natural phenomena are not part of the definition of the word pollution as it is used here.

The world’s oceans are subject to many incidences of direct pollution, caused by human activity taking place on its surface, in its waters and on its shores.

Pibalour fishing

Pollution en route to the sea

All forms of human activity are the source of specific types of pollution. Urban areas produce solid and liquid waste, part of which enters the water system. Industrial facilities deliberately
or accidentally release chemicals into the drainage network. Land washing by rainfall sweeps fertilisers and pesticides from agricultural fields into the water system. Transport accidents occasionally pollute rivers and streams. All these forms of pollution are carried by the water system into estuaries and finally into the sea.

More information

Everything flows into the sea


These activities, such as maritime transport, fishing, aquaculture, tourism, exploitation of sand and gravel, underwater drilling, coastal industries, national defence activities, bring varying quantities of mineral, organic, chemical and radioactive discharge, in the form of solids, liquids or gases.

However, in many coastal areas, the impact of these direct discharges at sea is minimal in comparison to pollution from the water system and atmospheric movements. Air pollution from industrial, automotive and urban sources and discharge into rivers from household, industrial and agricultural sources, for the most part end up in the sea.

More information

Water pollution: Industrial and institutional wastes and other harmful or objectionable material in sufficient quantities to result in a measurable degradation of the water quality.
(Source: Environment Canada’s on-line glossary. Reproduced with the permission of the Minister of Public Works and Government Services, 2006.)

Pollution of the marine environment: the introduction by man, directly or indirectly, of substances or energy into the marine environment which results or is likely to result in such deleterious effects as harm to living resources and marine life, hazards to human health, hindrance to marine activities, including fishing and other legitimate uses of the sea, impairment of quality for use of sea water and reduction of amenities.
(Source: United Nations Convention on the Law of the Sea)