International Center for Environmental
Management of Enclosed Coastal Seas
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The World's Enclosed Coastal Seas

The Environmental Management of Enclosed Coastal Seas Protecting Our Coastal Seas for Future Generations

The World’s Major Enclosed Coastal Seas

In many parts of the world there are bodies of sea water that are almost entirely enclosed by land. These bodies of water are called enclosed coastal seas. Examples include the Mediterranean Sea, the Baltic Sea, Chesapeake Bay, the Gulf of Thailand, the Bo Hai in northern China and, in Japan, the Seto Inland Sea, Tokyo Bay and Ise Bay. Since ancient times, enclosed coastal seas have been known for their great scenic beauty. Their outstanding natural attributes have spurred the development of transportation networks and many types of industry in the ocean and coastal regions, and they have been the setting for cultural and recreational activities throughout the ages. But man’s activities have exceeded the natural ability of the seas to cleanse themselves, giving rise to problems of pollution in the world’s enclosed coastal seas such as eutrophication, “red tides” and “blue tides”. We must work to preserve these priceless natural treasures if we are to pass them onto future generations.

Major Enclosed Coastal Seas of the World

  1. Chesapeake Bay(11,603km2,6.4m)
  2. San Francisco Bay(1,040km2,6m)
  3. Gulf of Mexico(1,592,800km2,1,486m)
  4. Mediterranean Sea(2,536,000km2,>5,150m)
  5. North Sea(575,200km2,94m)
  6. Baltic Sea(422,200km2,55m)
  7. Persian Sea(233,000km2,35m)
  8. Gulf of Thailand(320,000km2,45m)
  9. Bohai Sea(77,284km2,26m)
  10. Seto Inland Sea(23,203km2,38m)
  11. Black Sea(508,000km2,1,240m)
  12. Puget Sound(2,600km2,>300m)
  13. Hudson Bay(1,232,300km2,128m)
  14. Gulf of California(153,000km2,1,200m)
  15. Caribbean Sea(2,718,200km2,2,647m)
  16. Red Sea(438,000km2,491m)
  17. Bay of Bengal(2,173,000km2,2,600m)
  18. South China Sea(2,319,000km2,1,652m)
  19. Yellow Sea(466,200km2,40m)
  20. East China Sea(735,800km2,175m)
  21. Sea of Japan(978,000km2,1,752m)
  22. Gulf of Carpentaria(370,000km2,60m)

※area, average depth, > maximum depth

Environmental Guidebook on the Enclosed Coastal Seas of the World(9MB/PDF)

Enclosed Coastal Seas in the World.pdf

No Sea area Dimensions Main Environmental
Protection Measures
Related Organizations and NGOs 1.Area Guide
2.Current Status and New Directions
1 Chesapeake Bay Surface Area 11,603km2
Volume 68.1km3
Average Depth 6.4m
  • 29 % were met the water quality standards (DO, transparency, Chl-a, underwater grasses)
  • Overabundance of N & P from air, land and water
  • Sedimentation into sea floor
  • Toxic chemicals (pesticides, pharmaceuticals, PCBs)
1.Area Guide
2. Robert M. Summers, 2018.
2 San Francisco Bay Surface Area 1,040km2
Volume 7km3
Average Depth 6m
  • Water quality of Bay has improved
  • Bottom sediment (70% were toxic to aquatic organisms)
  • PCBs, methyl mercury and dioxin are highly detected in fish
  • Decrease and regeneration of Habitats
  • Decline of biological resources
1.Area Guide
3 Gulf of Mexico Surface Area 1,592,800km2
Volume 2,366,901km3
Average Depth 1,486m
  • Loss of coastal wetland
  • Fish contaminants
  • Sediment quality
  • Oil spills
1.Area Guide
4 Mediterranean Sea Surface Area 2,536,000km2
Volume 3,750,000km3
Average Depth -
  • Eutrophication, heavy metals pollution, organic pollution, microbial pollution (coastal areas)
  • POPs
  • Marine litter
  • Marine noise
1.Area Guide
5 North Sea Surface Area 575,200km2
Volume 54,069km3
Average Depth 94m
  • Eutrophication
  • Contamination by trace organic compounds
  • Marine litter
  • Impacts of climate change
  • Damage to shallow sediment habitats
1.Area Guide
2. Jean-Paul Ductoroy, 2018.
6 Baltic Sea Surface Area 422,200km2
Volume 23,221km3
Average Depth 55m
  • Eutrophication
  • Pollution by hazardous substances
  • Oil pollution
  • Threat to biodiversity
1.Area Guide
7 Persian Gulf Surface Area 233,000km2
Volume 8,155km3
Average Depth 35m
  • Oil pollution
  • Land-based pollution
  • Destruction of habitats
1.Area Guide
8 Gulf of Thailand Surface Area 320,000km2
Volume 14,400km3
Average Depth 45m
  • Water quality of Main river
    Chao Praya; deteriorated
    Tha Chin; deteriorated
    Mae Klong; fair
    Bangpakong; fair
  • Pollution in the Gulf (mercury)
  • Sediment quality (heavy metals)
  • Degradation and decline of habitats
  • Reduction of coral reefs
1.Area Guide
2. Menasveta, P.,Chavanich, S., Jarupongskul, T., 2019.
9 Bohai Sea Surface Area 77,284km2
Volume 2,009km3
Average Depth 26m
  • Nearshore areas (pollution of organic matters, active phosphate, petroleum hydrocarbon, inorganic nitrogen and heavy metals)
  • Red tides
  • Oil spills
  • Coastal erosion
  • Blue Sea Action Plan for the Bohai Sea
1.Area Guide
2. Yanfang Li, 2019.
10 Seto Inland Sea Surface Area 23,203km2
Volume 881.5km3
Average Depth 38m
  • Water quality (COD, TP and TN pollution from land has been greatly reduced)
  • Red tides (200-300 in 1975, 100 in recent year)
  • Reduction of neritic region
1.Area Guide
2.Osamu Matuda, 2017.
11 Black Sea Surface Area 508,000km2
Volume 629,920km3
Average Depth 1,240m
  • Invasive species
  • Land reclamation
  • Change wettland to agricultural polder
1.Area Guide
2.Ruben Kosyan, 2019.
12 Puget Sound Surface Area 2,600km2
Volume 169km3
Average Depth -
  • Low dissolved oxygen
  • High fecal coliform bacteria contamination
  • Eutrophication
  • Chemical contamination (PCBs, DDT)
  • Sediment (arsenic, copper, mercury, lead and zinc)
  • Shoreline modification
1.Area Guide
13 Hudson Bay Surface Area 1,232,300km2
Volume 157,734km3
Average Depth 128m
  • Ecosystem pollution (organochlorine; DDT, PCBs radionuclides; Cs-137)
  • Climate change
1.Area Guide
14 Gulf of California Surface Area 153,000km2
Volume 183,600km3
Average Depth 1,200m
  • Fish reproduction (high salinity)
  • Pesticide input from agricultural area
  • Species in danger of economic extinction
  • Greater local control over marine resources
  • more law enforcement in the government
  • USA provides finantial assistance for the environmental protection of the Gulf
  • To develop public educational materials
  • Sea of Cortez International Preservation Foundation
1.Area Guide
15 Caribbean Sea Surface Area 2,718,200km2
Volume 7,195,075km3
Average Depth 2,647m
  • Water pollution (sewage, eutrophication)
  • Degradation of seagrass and coral reefs
  • POPs
  • Solid waste
  • Offshore oil and gas exploitation are sources of pollution
  • Habitat destruction due to coastal development
1.Area Guide
16 Red Sea Surface Area 438,000km2
Volume 215,058km3
Average Depth 491m
  • Pollution comes from land-based activities
  • Oil exploitation
  • Destraction of habitat
  • Over exploitation of marine resources
1.Area Guide
17 Bay of Bengal Surface Area 2,173,000km2
Volume 5,649,800km3
Average Depth 2,600m
  • Pollution in the Bay is localized (eutrophication, POPs)
  • 1,800 ton/year of pesticides enter the Bay
  • Oil pollution (offshore oil and gas exploration)
  • Seabed mining
1.Area Guide
18 South China Sea Surface Area 2,319,000km2
Volume 3,830,988km3
Average Depth 1,652m
  • Water pollution (sewage, BOD, eutrophication)
  • Trans Boundary Issues associated with Regional Food Security
  • Threats to coral reefs
1.Area Guide
19 Yellow Sea Surface Area 466,200km2
Volume 18,648km3
Average Depth 40m
  • Water Quality (general good)
  • Sediment Quality (High organic concentration)
  • Over exploitation of fishery resources
  • Harmuful Algal Blooms (HAB)
  • Strict controls on fishing efforts
  • Transboundary cooperation (NOWPAP, TRADP, APEC, GEF/UNDP/IMO)
1.Area Guide
20 East China Sea Surface Area 735,800km2
Volume 128,765km3
Average Depth 175m
  • Urbanization and industrialization accerated environmental pollution and water quality deterioration
  • Sediment quality (not serious polluted)
1.Area Guide
2.Zhongyuan Chen, 2019.
21 Sea of Japan Surface Area 978,000km2
Volume 1,713,456km3
Average Depth 1,752m
  • Red Tides
  • Influence of global warming
  • Marine litter
  • Radioactive pollution
  • Oil spill
  • Ongoing environmental protection measure
  • Northwest Pacific Action Plan (NOWPAP)
  • Coastal Marine litter Survey
1.Area Guide
22 Gulf of Carpentaria Surface Area 370,000km2 Volume 22,200km3 Average Depth 60m
  • Marine debris
  • Rising sea temperature by climate change
1. Ruth Patterson, 2019.
New! 2. Improving certainty in marine ecosystems: A biophysical modelling approach in the remote, data-limited Gulf of Carpentaria