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Water contamination level in Osaka City in 2005 (excerpt from White Paper on the Environment, Osaka City, 2006 edition)
So what is the actual quality of water of the rivers in Osaka today? According to the 2006 edition of the Osaka City’s White Paper on the Environment, the annual average BOD (Biochemical Oxygen Demand) for the city’s twelve rivers and streams was 2.8 mg/L, which, compared to 10 mg/L in the 1970s, has been dramatically reduced. In some rivers such as the Neya River and the Hirano River, however, the BOD level is still considerably high, ranging from 8.1 to 13 mg/L. At a point near the Tenjin Bridge, where those rivers merge into the Okawa River, the water contamination exceeds the environmentally acceptable level (3.2 mg/L for the Dojima River (north stream of the Okawa River); 5.4 mg/L for the Tosabori River (south stream of the Okawa River)).
Consider the Dotonbori Canal, which became infamous as a place into which fans of the Hanshin Tigers, a local professional baseball team, dived when the team won the championship. Since the development of new canal locks began in 2000, the quality of the water of Dotonbori has improved remarkably. Two canal locks, one at the downstream end of the Dotonbori Canal and the other at the Higashi-Yokobori Canal, open and close according to tidal changes in Osaka Bay, preventing the flow of contaminated water from the Neya River and releasing cleaner water from the Okawa River to the canals. The locks are also effective in maintaining the water level and protecting the city from being flooded by seawater. In 2005, the average BOD of the Dotonbori Canal was recorded at 2.3 mg/L, showing the successful improvement of the water quality. So is the canal safe and clean enough to jump in and swim in now? The answer is no–the stream still contains a high level of E. Coli and other bacteria, because the current sewage system allows wastewater from neighborhood bathrooms and kitchens to flow into the canal during heavy rain. Are there any possible solutions for this problem? According to the Public Works Bureau of Osaka City, the city expects a dramatic improvement in the water quality of Dotonbori once the ongoing construction of the Kitahama-Osaka rainwater reservoir is completed in 2010 to cease the flow of rainwater into the canal. The city has conducted other improvement projects as well, such as more frequent dredging of sewage pipes. I would say the situation regarding Osaka’s symbolic canal looks promising.
