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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.

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.

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!


1. Create canal flow at the bottom of Tokyo Bay by using the daily tide.

2. Improve water and canal bottoms qualities by, for example, aeration.

3. Diverse the sewage plants and utilize the nutrients rich water from the plants for agriculture and vegetation through the basin.

4. Reform the land used of the store building area to wetlands or beaches.


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 Environmental NGO.


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