| Type | Primary Source/Cause | Effect |
| Nutrients | Runoff approximately 50% sewage, 50% from forestry, farming, and other land use. Also airborne nitrogen oxides from power plants, cars etc. | Feed algal blooms in coastal waters. Decomposing algae depletes water of oxygen, killing other marine life. Can spur algal blooms (red tides), releasing toxins that can kill fish and poison people. |
| Sediments | Erosion from mining, forestry, farming, and other land-use; coastal dredging and mining | Cloud water; impede photosynthesis below surface waters. Clog gills of fish. Smother and bury coastal ecosystems. Carry toxins and excess nutrients. |
| Pathogens | Sewage, livestock. | Contaminate coastal swiming areas and seafood, spreading cholera, typhoid and other diseases. |
| Alien Species | Several thousand per day transported in ballast water; also spread through canals linking bodies of water and fishery enhancement projects. | Outcompete native species and reduce biological diversity. Introduce new marine diceases. Associated with increased incidence of red tides and other algal blooms. Problem in major ports. |
| Persistent Toxins (PCBs, Heavy metals, DDT etc.) | Industrial discharge; wastewater discharge from cities; pesticides from farms, forests, home use etc.; seepage from landfills. | poison or cause disease in coastal marine life, especially near major cities or industry. Contaminate seafood. Fat-soluble toxins that bio-accumulate in predators can cause disease and reproductive failure. |
| Oil | 46% from cars, heavy machinery, industry, other land-based sources; 32% from oil tanker operations and other shipping; 13% from accidents at sea; also offshore oil drilling and natural seepage. | Low level contamination can kill larvae and cause disease in marine life. Oil slicks kill marine life, especially in coastal habitats. Tar balls from coagulated oil litter beaches and coastal habitat. Oil pollution is down 60% from 1981. |
| Plastics | Fishing nets; cargo and cruise ships; beach litter; wastes from plastics industry and landfills. | Discard fishing gear continues to catch fish. Other plastic debris entangles marine life or is mistaken for food. Plastics litter beaches and coasts and may persist for 200 to 400 years. |
| Radioactive substances | Discarded nuclear submarine and military waste; atmospheric fallout; also industrial wastes. | Hot spots of radio activity. Can enter food chain and cause disease in marine life. Concentrate in top predators and shellfish, which are eaten by people. |
| Thermal | Cooling water from power plants and industrial sites | Kill off corals and other temperature sensitive sedentary species. Displace other marine life. |
| Noise | Supertankers, other large vessels and machinery | Can be heard thousands of kilometers away under water. May stress and disrupt marine life. |
Source: Compiled by WorldWatch Institute.
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