Japan · Rivers


Guest Blog by Aparna Datar

The Ayu (sweetfishPlecoglossus altivelis) is a freshwater fish, a much loved symbol of the clearest streams of Japan. It’s remarkable come back, against the steep odds stacked against it, reflects in many ways, its own behavior of swimming against tide. Although a native of Gifu prefecture, it however grandstands as a cultural Hero in Tokyo’s astonishing and heartwarming story of people, river and yes… the Sewers!

Gifu Prefecture
GIfu Prefecture (Source: Wikipedia)

All great outbreaks run their course gradually, but the Ayu’s course was the opposite, from a certain existential die off, to a spectacular comeback. The Ayu’s story is the story of Tokyo, pulling itself back from the brink of collapse of the health of its people, its creatures and it’s Rivers.

The Tokyo Metropolitan Government conducts an annual census, for the last few decades now, and this summer (June 2108) it found that, the largest number of Ayu till date, decided to grace Tokyo’s Tama River[i].

Tokyo (Source: Wikipedia)
Tamagawa running thru Tokyo
Tamagawa running thru Tokyo (Source: Getty Images)

The Tama Gawa (river) starts in the mountains of the Yamanashi prefecture in central Japan and flows into the capital dividing it between Tokyo, Kawasaki and Kanagawa.

The Tama and her Satoyamas[ii] are home to several other species of birds, plants and fish besides the Ayu. Most of them are local but many are foreign and invasive to the Tama as well (which is another story for another time!).

Satoyama on banks of tama
A Satoyama on banks of the Tama (Photo by: Aparna Datar)

One of the representative pit stops for understanding the Tama and her Ayu is the stretch that runs through Tokyo’s Setagaya ward. Its banks teem with ducks, herons, egrets, turtles and even seals. The most populous of all of the Tokyo Metro’s 23 wards, a modern futuristic metro, that houses many of Tokyo’s plushest neighborhoods, Setagaya is home to movie stars, baseball players and kabuki actors.

 Setagaya’s most beloved resident however lives inside the Tama river that runs through it. The Ayu, the Princeling of the fresh waters.

Signboard displaying the fish of the Tama in the stretch
Signboard displaying the fish of the Tama in the stretch

The Tama is a class A river, which means the central government is the owner/manager of the river) Her banks are split into 8 zones[iii] and many parts of the Setagaya stretch are zones 3, 4 and 5[iv], i.e. spaces designated for activities like walking, swimming, and a “nature sensitivity zone” as the Tama River Basin Plan calls them. People enjoy the bounty of flora and fauna, nature enthusiasts, conservationist and biologists conduct their River Schools. Then there are ecological zones (the Nagata city stretch near the Yokota Air Base, an American naval base, is closest to Setagaya) which are basically, protected habitats of plants animals and riverine life. The idea is to restore the ecological health of this zone to the original condition.

fish orphanage
Invasive Fish Species Orphange for citizens at Satoyama

Summer is when the Ayu takes center stage here, when it spawns. The 140 km Tama stretch and its Satoyamas are a festa of river schools run by environmental experts and nature lovers, children spending the unusually long days at these.  Conservationists snorkel to enjoy this veritable treasure of the Ayu fish, marveling at the astonishing abundance of the Ayu.

This year more than 9 950 000 Ayu graced the Tama[v]! The Ayu is a gift of the Tama alone and no other river has managed to duplicate this phenomenon. Nowhere in Japan indeed anywhere in the world do so many Ayu exist in one river.

Ayu Uzu Koshi
Ayu Uzu Koshi by Japan’s iconic painter Hiroshige. Painted in early 1800s. Source: Library of Congress

Even in the more pristine Rivers of the Gifu region, large ones like the Nagaragawa, the Ibigawa and the Kiso where Ayu is originally from, these large numbers of the Ayu, will be quite impossible to come by.

In many municipalities of rural Gifu treating water is only, but a legal requirement for supplying to residents. The water that goes in and comes out is of the same quality. The Ayu is an important part of ecological and cultural triumphs of Tokyo.

The reason is that, the Tama is a veritable store house of algae, that the Ayu feeds upon. It is present in such abundance the fish have lost their territorial nature. Swathes and swathes of them can be found in close proximity of each other, a phenomena entirely unique to the Tama. This has further helped to explode its numbers.

Why does so much Algae thrive in the Tama alone? Why is Ayu such a central part of Tokyo’s urban resurgence?  Come spring and several industrial conglomerates will be outdoing each other in a billboard war trying to burnish their green credentials on the Ayu’s little back.

The answer lies in much destruction and disease wrought by the Tama on her own creatures and people, four decades back.


The Tama in the 60s
Tama in the 60s. Source: screen shot of an NHK documentary on the Setagaya ward

In 1960 the Tama was called the river of Death.

The Tama was both a source of Ayu and Gravel to Tokyo from the 1600s onwards. The post war era for Setagaya and Kawasaki and consequently the Tama was one of great industrial and population growth. Japan was growing at a rate that exceeded 9 %.

The Tama resembled the Bellandaur lakes or the like, of present day Bangalore. Foam covered the river upto a height of 1 meter. Heavy eutrophication existed in many parts of the river. A foul stink hung heavy, foam attacking homes and expressways.

Population exploded and household sewage, synthetic detergents, untreated industrial effluents, including heavy metals, mercury, phosphates, cadmium were released straight into the river. There was no sign of oxygen in the river. It was a dystopian past, that can by no stretch of imagination, be associated with the present-day neighborhoods of the Tama.

The fish died en masse, as did the algae and any aquatic life that thrive so plentiful today inside the Tama. Japan’s greatest health crisis came from the untreated sewage, the heavy metals inside the river.

Dangerous diseases like the Itai-itai disease[vi], the Minamata[vii] causing much human suffering attacked Japan. The financial burden of disease hovered at Yen 500 million annually. Tokyo bay was heavily suffering from hypoxia. In 1970 the water purification plant in Setagaya ceased to operate because, the water of the Tama was considered dangerous and unfit for human consumption.

Gravel on which carps now lay eggs was mined for centuries, at unforgiving rates. The mining area became a sediment trap where gravel from upstream started to settle reducing the amount reaching downstream. A dam was also constructed on the Tama, that further magnified this impact. The Tama got deeper and narrower. Mining was eventually outlawed in early 50s. But the damage was done. The Ayu did not like visiting the now deepened waters.

Following the crisis, far reaching legislative changes were brought in the 60s and the 70s. A new River law was drafted and environment was made one of the objectives through this law. Tokyo invested in a massive state of the art sewage system and the fortunes of its people and creatures changed, and how!

Presently Tokyo spends 5% of the TMG (Tokyo Metropolitan Government) budget on sanitation and health. They say the sewage network length can reach Sydney and back …twice! More than 400 million cubic meters of recycled treated water is drained annually into the Tama[viii] today. The TMG considers the amount of sullage equivalent[ix] of the amount of water used by household when it charges the city for treating sullage and supplying water to households. 900,000 people live in Setagaya.[x] Within the reaction chambers of Tokyo’s massive sewage infrastructure sludge is left at the mercy of microorganism, eventually incarcerated, the ash used to construct sewage pipes. The treated Sewage is released back into the Tama. It accounts for 60 percent of Tama’s water, her most important water source.


The Tama Today
The Tama Today (Photo by Aparna Datar)

This made possible the comeback of the Ayu and over sixty odd species[xi] of fish and the aquatic marine life. The Kingfisher or the Egret feeding on the Ayu now became a logo on many of the waste water recycling plants in Tokyo, indeed a symbol of Tokyo’s ecological and cultural triumph.

This recycled sewage is the secret of the phenomenal amount of algae that the Ayu feed on. The sewage treatment widely considered effective in every kind of pollutant, fails to take away the nitrogen and phosphorus compounds in entirety. This nitrogen and the phosphate is the secret of the wild abundance of algae upon which the Ayu feed. The Algae thrives upon it. The sewers of this gargantuan metro, eke out this food source for the algae, into the river to keep the growth rate of the Algae at an astonishingly high rate viz. even the most pristine waters in Ayu’s original habitat.

This balance of Riverine ecology has been instrumental to keeping the Tama clean. In absence of the fish, this phenomenal amount of algae and other aquatic plants might have decayed and destroyed the river. But the presence of the Ayu keeps the river near perfect on the oxygen level front.


Egret catching Ayu
Egret catching Ayu (Photo: Getty Images)

The Ayu travel upstream against the current every spring. One of the scintillating features of the New Tama River Basin Plan that was brought in, was to remove several weirs that obstructed the fish movement upstream, that had been built on the Tama. This in turn propelled many conservation activities.

In the Setagaya stretch of the river 4 big weirs have been removed. The gates of the remaining weirs are opened, always in consultation with citizens during the Spring, when the fish travel upstream. Carps, Ayu and several other species have benefited.

Where weirs cannot be removed, changes have been carried out. Some of the weirs now built are an “Ice Cone Style Weir” where the current is maintained in the middle, just so that the fish can rest, as it travels, or a half cone style weir that is designed to prevent a shock to the fish as they fall, and sand does not accumulate on their route.

 Citizens actively engage in small changes along the way that will make the fish travel upstream easier. Ladders are constructed or sandbags filled with gravel are piled up high in places to direct the flow in a certain way so fish find the journey just that one bit easy.

Through the decade of the eighties, economic compulsions moved manufacturing out of Kawasaki, and into China. Factories and manufacturing units were replaced with shopping malls and residential complexes. This also played into helping the cause of the Ayu coming back home to the Tama.

Tokyo has nursed the Tama back from the dead. The River of Death or the Shi no Kawa has turned into a spring well for life. There are lessons here for other Urban Rivers.

Aparna Datar (aparnanitindatar@gmail.com)


[i] https://www.nikkei.com/article/DGXMZO31278970R00C18A6L83000/

[ii] https://en.wikipedia.org/wiki/Satoyama

[iii] http://www.ktr.mlit.go.jp/keihin/index.html

[iv] http://www.metro.tokyo.jp/index.html

[v]  https://www.nikkei.com/article/DGXMZO31278970R00C18A6L83000/

[vi] https://en.wikipedia.org/wiki/Itai-itai_disease

[vii] https://en.wikipedia.org/wiki/Minamata_disease

[viii] http://www.mlit.go.jp

[ix] http://www.gesui.metro.tokyo.jp/index.html

[x] https://en.wikipedia.org/wiki/Setagaya

[xi] http://www.ktr.mlit.go.jp/keihin/index.html

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