With an area of 670,4 square kilometers, it is located on the island of Honshu - also the country's largest - and is often mentioned both in Japanese literature and in the media for a series of environmental crises.
The latter was revealed by finding that its bottom was filled with garbage, 70% of it plastic.
Reports from diver surveys in 2020 said that among the finds was a bag estimated to date back to before the 90s.
Environmental crime, however, in this endemic species-rich ecosystem had started much earlier, since the 60s.
At the time, the concern was limited to managing the unpredictable water levels on which millions of people depended in the metropolitan area between Kyoto, Osaka and Kobe - today the second most populous region in Japan.
In the later years of Japan's rapid economic development, huge factories were built on the shores of the lake, consuming countless amounts of water.
Large-scale industrial production and agriculture in the surrounding area have resulted in Biva being "poisoned" with pesticides, heavy metals and other harmful substances.
By the end of the 70s, huge colonies of red algae appeared, rapidly "swallowing" the oxygen in the water.
Combined with fishing, they led to the extinction of large quantities of fish and shellfish.
It took until 1980 to place an ordinance limit on the "jewel" lake for nitrogen and phosphorus levels from industrial, agricultural or domestic use.
But that wasn't enough….
Looking for solutions
In the 40 years since then, significant investments have been made in infrastructure, with a focus on the construction of new sewage treatment plants.
Since 1992, the preservation of the reed beds, once a trademark of the lake, has been ordered, but has now halved.
Their role is pivotal in water purification, while they are a place for bird and fish nests.
Από το 1993, η λίμνη Μπίβα εντάχθηκε στη Συνθήκη Ραμσάρ της UNESCO για την προστασία πολύτιμων υδροβιότοπων.
Thus, from the beginning of the 90s, the carp and trout populations began to stabilize.
Nevertheless, they remain less than a tenth of what they were for most of the 20th century.
Episodes of eutrophication - the excessive growth of plants in the aquatic ecosystem - have however decreased and are now considered rare.
Nevertheless, the disturbance of the environmental balances led in the meantime to an increase in the number of threatened species in the wider area.
From 74 in 2000, they reached 2020 in 156.
They range from woodpeckers, to frogs: species that live in or depend on lake ecosystems.
Meanwhile, new challenges have arisen over the years.
The most acute is the pollution of Biva by plastics.
The extent of the problem was established by underwater surveys. However, the exact dimensions and consequences it has on the lake's ecosystems remain to be ascertained.
Concerns are already intensifying about the effects of microplastics.
Relevant research is being carried out, within the framework of initiatives of the Biva Center for Environmental Sciences Research.
Many have been implemented since the beginning of this month.
The aim is to have a complete picture of the overall situation and coordination with the regional authorities.
In the meantime, other "unknown X's" are added to the "equation".
Among the new demands is to determine the "footprint" of climate change on the lake and to predict how and how much extreme weather events may worsen the situation in Biwa.
Εάν και πόσες επιβλαβείς ουσίες φέρουν για παράδειγμα τη λίμνη οι floods από τις έντονες βροχοπτώσεις, που «φουσκώνουν» τα 118 ρυάκια, χειμάρους και μικρά ποτάμια, τα οποία πηγάζουν από τα γύρω βουνά, προτού περίσσεια νερού στη Μπίβα διοχετευτεί στον ποταμό Σέτα.
Η αύξηση της θερμοwineας των υδάτων από την άλλη έχει ως αποτέλεσμα απώλειες οξυγόνου.
In any case, the problems are not limited to the borders of the lake.
The environmental degradation of the surrounding areas, from the mountains to the agricultural lands, make up a complex management of the region's ecosystems, while urbanization becomes more and more intense.
It is against this background that the authorities in Shiga prefecture - where Biwa is located - have already set 13 targets for the "Mother Lake".
They include measures aimed at reducing greenhouse gas emissions to supporting initiatives to protect ecosystems.
Already groups of volunteers are participating in operations to remove harmful aquatic plants from Biwa.
Fishing industry organizations are creating new reed beds in shallow waters.
Businesses are encouraged to adopt green practices through certifications and subsidies.
For the first time since 1975, tree planting was organized in the mountains of Shiga last spring.
There are campaigns to improve the conditions on the shores of the lake, to clean its bottom from plastics, as well as to remove waste from the surrounding lands.
The road to recovery is still long, but promising.
Not only for Biwa, but also for other areas, where leaders and residents really have the will to solve chronic problems, which they themselves have created over the years.