The Environment Ministry on Thursday called on Nagasaki Prefecture to ensure that water quality inside the seawall of the controversial Isahaya Bay reclamation project falls within acceptable levels.

The move follows a revision of the project that simulations indicate will bring water quality dangerously close to exceeding acceptable levels of total nitrogen, total phosphorous and chemical oxygen demand — all indications of poor water quality.

In July, Nagasaki Prefecture approved a plan to halve the planned reclamation area to 900 hectares and increase the water area on the inside of the nearly 7-km seawall. by the same amount to 2,600 hectares.

With enhanced planting of reeds around the inner body of water, simulations indicate that chemical oxygen demand will reach up to 4.9 parts per million, just below the environmental limit of 5 ppm. The same is true of total phosphorous, which is projected to reach up to 0.098 ppm, compared with the acceptable upper limit of 0.1 ppm.

Reeds improve water quality by minimizing the amount of material that swirls around in shallow water due to winds, officials said.

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