Tokyo Bay, Osaka Bay, Lake Biwa, and Lake Kasumigaura Water Pollution - 2020s

Tokyo Bay, Osaka Bay, Lake Biwa, and Lake Kasumigaura Water Pollution - 2020s

In the 2020s, water pollution in Japan's coastal and inland waters remains a serious issue. Especially in areas such as Tokyo Bay and Osaka Bay, as well as major lakes like Lake Biwa and Lake Kasumigaura, pollution levels are particularly high. According to a 2020 survey, the Chemical Oxygen Demand (COD) in Tokyo Bay reached 7.4mg/L, and in Osaka Bay, it was 6.9mg/L, both of which significantly exceed the national standards, indicating persistent water quality degradation.

In Lake Biwa (Shiga Prefecture), the concentrations of total nitrogen and total phosphorus have remained high, contributing to ongoing eutrophication. A 2021 survey reported total nitrogen levels of 1.5mg/L in the northern part of the lake and 2.0mg/L in the southern part. Total phosphorus levels were 0.10mg/L and 0.12mg/L, respectively, with abnormal algae blooms (Aoko) still occurring. Similarly, in Lake Kasumigaura (Ibaraki Prefecture), COD levels reached 10.5mg/L, marking one of the worst cases of lake pollution in Japan, and the effects on ecosystems from eutrophication are a growing concern.

One of the main causes of this water pollution remains the insufficient treatment of household wastewater. In Tokyo Bay, untreated household wastewater and rainwater flowing from the Tama and Arakawa Rivers are significant sources of pollution. Additionally, industrial wastewater discharged from petrochemical complexes around Ichihara City (Chiba Prefecture) and Kawasaki City also contribute to the issue. Major companies such as **JXTG Energy** (now **ENEOS Holdings**) and **Showa Denko** are working to strengthen environmental measures, but complete resolution remains challenging. In the Lake Biwa area, wastewater from food processing industries and agricultural runoff are problematic, with nitrogen and phosphorus from fertilizers accelerating eutrophication.

Moreover, microplastic pollution has become a new environmental challenge in the 2020s. In Tokyo Bay and Osaka Bay, high concentrations of microplastics are severely impacting marine ecosystems. A 2022 survey detected 0.8 microplastic particles per square meter in the coastal areas of Tokyo Bay, raising concerns about the impact on fish, shellfish, and potentially on human health through the food chain.

The Japanese government and the Ministry of the Environment have announced plans to further strengthen wastewater treatment infrastructure and enforce stricter regulations on industrial discharges. Companies like **ENEOS Holdings** and **Hitachi Zosen** are also introducing advanced water purification technologies, but widespread adoption is still slow. For example, **Hitachi Zosen** has started implementing next-generation biofilter purification systems in Lake Biwa, but scaling up these projects remains a challenge.

At the local level, the Shiga Prefecture government is promoting the "Lake Biwa Conservation and Restoration Plan," encouraging local farmers to reduce the use of chemical fertilizers and adopt environmentally friendly agricultural practices. However, to see real impact, stronger monitoring systems and long-term commitment are needed, and these challenges remain ongoing.