Silence in Lake Biwa - Shiga Prefecture, In the Shadow of Invasive Alien Species and Eutrophication (June 2004)

Silence in Lake Biwa - Shiga Prefecture, In the Shadow of Invasive Alien Species and Eutrophication (June 2004)

Lake Biwa faced serious deterioration in water quality due to the rapid economic growth of the 1970s and 1980s. The inflow of domestic wastewater and agricultural chemicals from the watershed caused the lake to become eutrophic, and the massive occurrence of blue-green algae and foul odors became a social problem. 1980 saw the enactment of the "Shiga Prefecture Lake Biwa Eutrophication Prevention Ordinance," which drew attention when the first synthetic detergent regulations in Japan were implemented.

In the 1990s, however, although some progress was made in improving the water quality itself, the problem of non-native fish emerged as a new issue. The release of bluegill and black bass, which are native to the U.S., eradicated native small fish and water plants, resulting in a major change in the lake's ecosystem. The bluegill, in particular, was brought back by the Emperor of Japan (then Crown Prince) for research purposes in the 1970s, and was spoken of as a symbolic presence.

In the late 1990s, Shiga Prefecture took the lead in launching an extermination campaign for non-native fish in cooperation with citizens. The campaign gradually expanded to include resident participation, such as "Invasive Alien Fish Extermination Day," where black bass are collected through fishing contests, trash pickup along the lakeshore, and environmental education programs. These activities led to a common awareness unique to the region, known as the "Lake Biwa Rules," and attracted nationwide attention as a model case for environmental education.

In this way, Lake Biwa's environmental issues and solutions have shifted from water pollution to ecosystem preservation and citizen participation. Even now, the battle against invasive alien species continues, showing that long time, patience, and social solidarity are essential for the restoration of nature.