Low Rainfall in Japan’s Kanto Region Sees Water Levels in Dams Drop, Exposing Typically Submerged Structures

The Yomiuri Shimbun

13:58 JST, February 7, 2026

A lack of rain is impacting the Kanto region, in contrast with the heavy snows affecting the Sea of Japan side of the country.

In Kanagawa Prefecture, the volume of water at some dams has dropped. Bridges and other structures that are typically submerged are now visible along the lakebed.

Due to the lack of rain since October, the total volume of water stored at three dams in the Sagami River system in Kanagawa Prefecture is only about half the average for the same period over the past 10 years.

Miyagase Dam, which supplies tap water to 21 municipalities including Yokohama, had a water storage rate of 41% as of Thursday. According to the Land, Infrastructure, Transport and Tourism Ministry’s office that manages the dam, rainfall last year was about 500 millimeters below average and the second lowest since the dam began operation in 2001. Monthly rainfall was lowest last year in November.

There was zero millimeters of rainfall recorded in January.

“At the moment, the situation is not at a stage that would cause disruption to daily life, but we ask people to use water resources sparingly,” said an official at the office.

At Lake Tsukui, an artificial lake created by Shiroyama Dam in Sagamihara, the water storage rate had fallen to 17% as of Thursday. Stone structures and what appear to be pillars, which are usually underwater, were also visible.

In the city of Mito, a drop in river water levels has prompted the growth of blue-green algae, leading to complaints that tap water smells moldy. Complaints began arriving at the city offices around January, and by Wednesday the number had reached about 100.

According to the Mito Regional Meteorological Observatory, the city of Mito saw zero millimeters of rainfall in January. This lack of rain has reduced the water level of the Naka River, which is the source of tap water for the city. The amount of water in the river in January fell to about 60% of the average level for the same month over the past 10 years, according to the land ministry’s local office that manages the river.

This has made it easier for sunlight to reach the riverbed, prompting the growth of blue-green algae that produce odorous substances, the city government said. But it stressed that the substances are not toxic, saying, “Tap water is safe to drink.”

In addition to the usual treatment at the water purification plant, the city government adds powdered activated carbon to absorb and remove the odor. However, a person in charge said, “It’s not enough to completely remove [the smell].” The odor is expected to remain until sufficient rain falls and the water level recovers.