A couple look upon Otsu city and Japan's largest lake, Lake Biwa, at an observatory in Otsu, Shiga prefecture in western Japan, April 6, 2012. Prefectures like Shiga, which have never been courted by the nuclear industry but lie close enough to reactors to be wary of them, are emerging as a serious complication for government and industry efforts to get nuclear power running again. Picture taken April 6, 2012. To match Analysis JAPAN-NUCLEAR/SHIGA REUTERS/Toru Hanai (JAPAN - Tags: ENERGY POLITICS)

Japan’s largest lake used to be a cesspool. Now it’s a vision of a sustainable future.

One day in 2021, veteran diver Kazumi Fujimoto was exploring Lake Biwa in search of ruins. Japan’s largest lake, and the third oldest in the world, contains over 100 historic lakebed sites concealed in its watery depths. But when he arrived at the site, it was covered in garbage and no longer visible. It was lost to history, even for skilled divers.

Lake Biwa, located smack-dab in the center of both Shiga Prefecture and the entire country, has long been a center of flourishing agriculture and cultural progress. The 670 square-kilometer lake is rich with endemic species, was a key source of civilization and farmland in Japan’s early Yayoi Period (200 B.C. to A.D. 250), and provides water supply for almost 15 million residents of the Kyoto-Osaka-Kobe megalopolis.

The lake has also been at the center of countless environmental crises.

In 2019, the northern part of Lake Biwa met national environmental standards for nitrogen concentration for the first time in decades. The improvement came after years of civil movements, new regulations and technological advances.

Abundant concerns remain: a decrease in aquatic life, a plastic litter crisis and the threat of climate change. But these same threats have led a determined network of agencies and volunteers to fight to keep their “mother lake” clean — offering a sustainable vision of resource management along the way.

A history of pollution

At the Biwa Environmental Sciences Research Center (LBERI), senior director Hiroshi Tsuno says that, from an ecological perspective, Lake Biwa can be seen as closer to an ocean than a lake.

“There are so many living things gathered here,” he says. “Our approach to research is to look at the whole system.”

Indeed, the countless rivers that feed into Lake Biwa and the mountain and forest habitats those rivers emerge from all affect the health of the lake and its water.

Tsuno explains that before pollution emerged as a crisis in the 1960s and 70s, managing the unpredictable water levels and flooding of a lake that countless people relied on was the primary concern. Then, during Japan’s periods of industrialization and rapid economic growth, Biwa’s water and lakeside went from being primarily used by local residents to being an essential resource for the entire Kansai region.

“Huge factories built around Kansai needed lots of water — and even more of it when there wasn’t enough to go around,” says Nobuhiko Miwa, chairman of Shiga Prefecture’s Lake Biwa Environment Bureau. Large-scale industry and agriculture caused pesticides, heavy metals and other harmful substances to enter the lake.

“This happened all over Japan, and is not unlike the substances that caused Minamata disease (in Kumamoto).”

Pollution started to reach its nadir around 1977, when huge red algal blooms appeared around the lake, killing massive numbers of fish. These blooms, known as eutrophication, happen when excess nutrients from fertilizer and chemicals enter the water.

The visual impact of eutrophication inspired direct civilian action. A powerful citizen’s movement formed to switch out synthetic household detergents, one of the main chemicals causing the blooms, for powdered soap. By 1980, a new ordinance helped curb the flow of nitrogen and phosphorus into Biwa.

Volunteers with the Umi o Tsukuru Kai group gather litter near Lake Biwa. | COURTESY OF UMI O TSUKURU KAI

Miwa explains that over the next 40 years, Shiga Prefecture invested heavily in infrastructure to build new wastewater treatment plants. A flurry of new laws through the late 1970s also created strict regulations for factory wastewater drainage.

“New infrastructure and regulations proved to be the fastest ways to reduce pollution to an impressive extent,” says Miwa. “We thought that these would be enough to solve the problem of pollution in the lake, but it turns out we need a lot more … including individual effort from all residents.”

Climate change looms large

According to the Lake Biwa Water Quality Preservation Organization (BYQ), levels of nitrogen have improved substantially since the early 1990s. Episodes of eutrophication have also declined and become relatively rare. On the other hand, chemical oxygen demand, which is used to measure the presence of organic pollutants in water, remains well over the national environmental standard.

“We can say that the water has become clean,” says Tsuno. “But that doesn’t mean the overall situation of the lake has gotten better.”

That is especially true for biodiversity and the fishing industry. Per data from Shiga Prefecture, total fishery catches, shellfish catches and catches for endemic fish species — such as trout and carp, the latter of which is used in Shiga’s traditional funazushi dish — have all dramatically declined since the 1950s. Shiga’s local Asian clams are no longer caught in significant numbers despite there being annual catches of well over 5,000 tons in the 1950s.

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