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Solutions to the triathlon water quality problem of Tokyo 2020 Olympic and Paralympic games

The cause of the water quality problem is recognized as eutrophication for the whole bay which drives algea bloom and subsequent anoxic water events. But, at the inner part of the bay locally, the overflow from sewerage plants after rain seems more significant than eutrophication. Measures to the sewerage plants which affect the triathlon swimming area of 2020 Olympic and Paralympic games are required. Among them the Shibaura and Mikawashima water reclamation centers are most important because of the location and quantity of treated water.

1. Solution which require no construction cost

For Shibaura water reclamation center which has the most influence on the water quality of the triathlon swimming area, the flow of the periphery canals could be controlled by the 5 water gates which surround the canals and by taking advantage of the tidal level fluctuation. It will prevent the diffusion of the sewerage water to the swimming area.






At the canals, always southward flow will be created and the canals located north than the center can be functioned as water purification area with aquatic plants. Further more the measure prevents sewerage water to flow upstream to Megurogawa and Furukawa rivers.

2. Solution which requires construction cost

Two sewerage centers which have the most influence to the area, the water discahrge points are desired to be dislocated where the water will not reached to the swimming area and will reach to the mouth of the bay as quick as possible. For the Shibaura water reclamation center it could be dislocated to off shore of the “Uminomori” and for the Mikawashima center it could be dislocated from Sumidagawa river to Arakawa river.




Sumidagawa river and the canals around Shinagawa   will start  functioning as water purification area which creates better environment for both the citizen and the living creatures.


The restoration of the Tokyo Bay is a dream of many people. Bring back the blue transparent Bay for the 2020 Olympic and Paralympic games as an legacy and revive the water city!



  • Observation, research and discussion about the Tokyo Bay especially the canals areas
  • Promote the dialogue between the stakeholders such as citizen, corporates and local governments
  • Submit opinions and proposals to the society

“Field Study by Walking!”
Every week we walk around the coast of Tokyo Bay for observation. Let’s walk together!

17 Sep 2016, Sat Meguro river to Takeshita pier (in Japanese)



Our actives are supported by the donations.
Please support us if you think it’s valuable!

Immediate needs: A laptop and diving equipments

Bank Account:
Sumitomo Mitsui Banking Corporation, Mita-Dori Branch, Saving account
Bank Code:0009, Branch number:623, Account Name: Blue Tokyo Bay, Account number: 8455632


1. Move the drain outlets of sewage plants to off the coast as far as possible instead of directly pouring to the canals which are surrounded by residences and commercial area. (Short-term solution)

2. Improve water and canal bottoms qualities by, for example, aeration. (Short-term solution)

3. Diverse the sewage plants and utilize the nutrients rich water from the plants for agriculture and vegetation through the basin. (Long-term solution)

4. Reform the land used of the store building area to wetlands or beaches. (Long-term solution)



Nobu Yamayoshi


About 20 years ago, when I worked on ships to help divers at marine consutracting sites in the Tokyo Bay, I saw the sludge from the bottom and thought “it must be done something for it”. I’ve been keeping the feeling and studied environment at graduate schools, then, I worked at WWF Japan. Just before the 2020 games, I start an organization to restore the environment of the Tokyo Bay. I think it’s time to do something.



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We have a dream!