Shiga Prefecture announced on the 7th that there were points where the amount of oxygen was less than 2 milligrams per liter, which is a guideline for affecting benthic organisms, in a survey of 7 points on the bottom of Lake Biwa from August to September. It has been 3 consecutive years since 2019. In February of this year, in Lake Biwa, the surface layer and the bottom of the lake were mixed, and the “full-thickness circulation” in which oxygen was distributed was confirmed for the first time in three years, but oxygen became insufficient in about half a year. No effects on living organisms have been confirmed.
The survey was conducted monthly by the Lake Biwa Environmental Science Research Center, and on August 30, the amount of oxygen at one site was 1.7 milligrams. On September 6th, it was 1.8 milligrams at another point. The amount of oxygen in Lake Biwa usually peaks in early spring and decreases, and recovers in the full-thickness circulation around February of the following year.