Women washing clothes in the Okawa River (photographed around 1936). Stone steps that led to the river near a boathouse were a perfect place to do the laundry. Photo courtesy of Osaka Castle

The driver of a water taxi, who is known for her enthusiasm for the improvement of Osaka's waterfront, once told me that the water of the rivers in Osaka is so polluted that if a woman falls in one of the rivers she won't be able to bear a baby. "I believe it's true," she insisted quite seriously as I replied to her with a doubtful look suggesting that I would only take her story as an unfounded rumor. It is still worth considering, however, the fact that Osaka's best self-proclaimed "waterfront lover" believes this gossip; as you look at the river water, it indeed appears kind of unsafe--scary enough to the eyes of us common people.

In fact, it has long been known that the rivers that run through Osaka City are prone to water contamination. The name of the Yodo River, for example, is believed to have originated from the word yodomu (to stagnate). The flow of the Okawa River (Kyu Yodo River) is slow and merges with other rivers and streams at its end. The urban development that ignored the existence of the rivers, in addition to the wastewater that the city continuously discharges, worsened the water pollution at an accelerated rate. Through the postwar period, the rivers in Osaka have turned into smelly, dirty, dangerous places and have had a negative press since then.

▼Click image to enlarge

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.

BOD (Biochemical Oxygen Demand)
BOD is used as the most common gage to indicate the quality and contamination level of river water. It shows the amount of oxygen needed within a certain period of time for biological organisms to decompose organic matter contained in water. The larger the figure, the worse the contamination.

February 12, 2008
Takuji Kobayashi
member of the board of directors, Suito Osaka-Mizubenomachi Saisei Project