|Primary inflows||31 small rivers of the Kiso Mountains|
|Primary outflows||Tenryū River|
|Surface area||13.3 km2 (5.1 sq mi)|
|Average depth||4.7 m (15 ft)|
|Max. depth||7.2 m (24 ft)|
|Shore length1||15.9 km (9.9 mi)|
|Surface elevation||759 m (2,490 ft)|
|Settlements||Okaya, Suwa, Shimosuwa|
|1 Shore length is not a well-defined measure.|
Lake Suwa is the site of a natural phenomenon known as the "God's Crossing" (御神渡り, o-miwatari), large cracks that form in the winter across the surface of the frozen lake. A vertical temperature gradient results in ice pressure ridges forming in the surface ice, reaching heights of 30 centimetres (1 ft) or more.
Local Shinto tradition holds that the ridges are formed by the gods crossing the lake when traveling between the various buildings of the Suwa Grand Shrine. Folklore says it is the guardian god of Suwa, Takeminakata-no-kami, leaving his sanctuary to meet with his wife, the goddess Yasakatome , joining the opposite bank by walking on frozen water. The record of this crossing is the oldest-known human-observed climate record. This record has been used by scientists to study the impact of sunspots, human development and anthropogenic CO2 emissions on lake ice formation.
The lake has a natural hot spring under its surface. Recreational development in the 1950s resulted in increased output from this underwater geyser. Since 1945, complete ice cover is considered to be achieved when the entire surface is frozen except for the opening in the ice for the geyser.
As a shallow lake, Lake Suwa is highly sensitive to climatic variation. Recent studies have shown that Suwa's ice-free years correlate to increasing atmospheric CO2 levels. Research on ice breakup at Suwa and at the mouth of the Torne River in Finland suggest that climate change is driving the changes in seasonal ice cover. As a result, it is expected that Lake Suwa will remain ice-free for almost the entirety of the 21st century's winters.
Epson, a global technology company, was founded and is headquartered in Suwa.
In popular culture
Sayo Masuda, author of Autobiography of a Geisha, was sold by her family to an okiya (geisha house) in Suwa at the age of 12. She tries to drown herself in the lake, but hesitates because she believes a dragon (possibly related to the omiwatari) inhabits it.
- In the anime Rurouni Kenshin, legend holds of an "Elixir of Immortality" that can be found somewhere in or around Lake Suwa. The main characters search for the elixir in the final season of the series and are followed by a band of evil German knights, seeking it for world domination.
- The anime Blood-C takes place in a rural town located on the shore of the lake.
- Suwako Moriya from Touhou Project is named after the lake.
- This lake is also popular because from the movie of Your Name as it gained its tourist visitors. The Itomori town where Mitsuha (Main Female Protagonist) lived was modeled after the Lake Suwa in Gifu.
- Arakawa, H. (1 June 1954). "Fujiwhara on five centuries of freezing dates of Lake Suwa in the Central Japan". Archiv für Meteorologie, Geophysik und Bioklimatologie, Serie B. 6 (1): 152–166. Bibcode:1954AMGBB...6..152A. doi:10.1007/BF02246747. Retrieved 25 October 2020.
- Takahiro, Nogami. "Encyclopedia of Shinto - Home : Shrines and Cultic Practices : Suwa Shinkō". eos.kokugakuin.ac.jp. Retrieved 25 October 2020.
- Sharma, Sapna; Magnuson, John J.; Batt, Ryan D.; Winslow, Luke A.; Korhonen, Johanna; Aono, Yasuyuki (April 2016). "Direct observations of ice seasonality reveal changes in climate over the past 320–570 years". Scientific Reports. 6 (1): 25061. Bibcode:2016NatSR...625061S. doi:10.1038/srep25061. PMC 4844970. PMID 27113125. Retrieved 25 October 2020.
- Tanaka, Minoru; Yoshino, Masatoshi M. (1982). "Re-Examination of the Climatic Change in Central Japan Based on Freezing Dates of Lake Suwa". Weather. 37 (9): 252–259. Bibcode:1982Wthr...37..252T. doi:10.1002/j.1477-8696.1982.tb03626.x. Retrieved 25 October 2020.
- Bell, Jillian (2016-04-27). "Industrial Revolution strongly tied to earlier thaws, later freezes: study". CBC News. Retrieved 2016-05-07.
- Filazzola, Alessandro; Blagrave, Kevin; Imrit, Mohammad Arshad; Sharma, Sapna (28 September 2020). "Climate Change Drives Increases in Extreme Events for Lake Ice in the Northern Hemisphere". Geophysical Research Letters. 47 (18). Bibcode:2020GeoRL..4789608F. doi:10.1029/2020GL089608.
- "Lake Suwa in Shinano Province (Shinshū Suwako), from the series Thirty-six Views of Mount Fuji (Fugaku sanjūrokkei) ca. 1830–32". www.metmuseum.org. Retrieved 25 October 2020.
- Masuda, Sayo (2005). Autobiography of a Geisha. New York. ISBN 0-231-12951-3.