Lake Kawaguchi Records Largest Water Drop in 29 Years Revealing Real Cause Behind Abnormal Situation Stirring SNS

Amid talks about declining dam water levels across the country due to consecutive days of little rainfall, an unbelievable sight is also unfolding at Lake Kawaguchi, one of Japan’s top tourist destinations. Normally, the “Rokkakudo” temple appears to float alone like an island, but now it has been possible to walk out to it for several days in a row.

The water level drop is −4.1 meters, an abnormal situation not seen in 29 years. On SNS, people are buzzing with comments like, “Has Mount Fuji’s spring water dried up?” or “Is this a sign of something?”—but the real cause lies somewhere completely different. Experts reveal the “unique circumstances of Lake Kawaguchi” and discuss the outlook going forward.

“As of March 6, the water level of Lake Kawaguchi is −4.1 meters. It’s rare for the water level to drop more than 4 meters; this is the first time in 29 years since 1997. Last year, the rainy season was short, and there were hardly any typhoons. This is thought to be due to the lack of rainfall.”

This explanation comes from Shinya Yamamoto, senior researcher at the Mount Fuji Volcano Disaster Prevention Research Center.

But isn’t the water of Lake Kawaguchi, and the other Fuji Five Lakes, fed by spring water from Mount Fuji?

“The water flowing into Lake Kawaguchi is not spring water from Mount Fuji, but underground water from the Misaka Mountain Range to the north, as well as the Teragawa River originating in the Misaka Range and the subterranean streams flowing beneath rivers that are now dry. When precipitation decreases, the amount of groundwater and subterranean flow entering the lake also decreases, causing water levels to drop.

When annual precipitation falls below 1,300 mm, there is a tendency for drastic water level drops. In 2025, the annual precipitation was around 1,080 mm, so it’s considered that the water level has dropped accordingly.”

However, groundwater takes decades or even centuries to flow through mountains before it surfaces. How does last year’s rainfall relate to this year’s drastic drop?

“Indeed, rain that falls last year may take decades or centuries to reach the surface. However, water accumulated underground is pushed out by last year’s rainfall, emerging as groundwater. When precipitation is low, groundwater is less easily pushed out, reducing the amount flowing into the lake, resulting in a major drop in water levels.”

Last year, the rainy season, which normally brings ample rainfall, was short, and there were few typhoons. As a result, the lake’s water level did not rise during summer and entered the winter low-water period with a drop of 4 meters.

According to Yamamoto, there are two other reasons for the low water levels besides the lack of rainfall.

One is leakage. Lake Kawaguchi is formed on lava, which has many cavities, making it easy for water to seep through, essentially creating natural leakage.

“However, this amount is very small. It does not cause a significant drop in water levels.”

The other reason is artificial drainage. Lake Kawaguchi is blocked by lava and has no natural outlet, so heavy rains can cause it to overflow. In the Meiji era, frequent floods caused damage to surrounding villages. To prevent this, drainage tunnels were built, and currently, two are in use. In spring, these tunnels are used to supply lake water downstream for agricultural purposes. However, if the lake’s water level drops below the bottom of the tunnels, water cannot be sent, potentially affecting farming.

It’s not just agriculture—shallow waters also prevent boats from operating, dealing a blow to tourism.

Is it safe for the water level to remain this low?

“If it starts raining in spring, it should be fine. In fact, in 2017, the water level also reached −3.7 meters. Although a drop of over 4 meters has occurred for the first time in 29 years, 2017 was only 40 centimeters higher than now. Once every ten years, the water level can drop significantly.”

The footage showing Rokkakudo connected to the shore is shocking, but for the past 10 years, this is a common sight during the winter-to-spring period when rainfall is low.

“Local residents and we are not worried because it is a scene we see in winter. In the past, winter temperatures often dropped to −10 to −15°C, and both Lake Kawaguchi and Lake Yamanaka would freeze completely. But recently, temperatures rarely fall below −10°C, and the lakes no longer freeze.”

Yamamoto says the warmer climate is unrelated to the water level, though some suggest that low rainfall may be influenced by global warming. Will we be able to see Lake Kawaguchi filled to the brim this summer?

▼Shinya Yamamoto – Senior Researcher, Mount Fuji Volcano Disaster Prevention Research Center, Mount Fuji Research Institute, Yamanashi Prefecture. He studies past environmental changes by analyzing organic compounds in sediments and their stable isotope ratios. His research focuses on the Fuji Five Lakes, investigating the history of Mount Fuji eruptions and their environmental impact. He also conducts geochemical investigations and analyses of groundwater in the Fuji Five Lakes and Mount Fuji to clarify the current natural environment of the area.