Case No. #1503
The Floating Lights of Chikubushima Island
Summary
Between September and October 2021, shrine priests and tourist boat passengers near Chikubushima Island in Lake Biwa, Shiga, reported eight sightings of luminous orange-to-white spheres (50 cm–1 m diameter) hovering above the lake surface. Multiple spheres appeared simultaneously in some cases. Lake bottom methane gas ignition ("lake fire") is a documented autumn phenomenon in Japanese lakes, but the scale and count of what was reported exceed typical descriptions. Chikubushima is a sacred island associated with Benzaiten and a tradition of floating lantern offerings.
Details
Chikubushima, a small island roughly 2 kilometers in circumference in the northern part of Lake Biwa, is a joint religious site of Tsukubusuma Shrine and Hōgonji Temple, long venerated as a sacred realm of Benzaiten. No general residents live on the island; only shrine priests and temple monks are stationed there year-round.
On the night of September 18, 2021, a shrine priest in his fifties watching the lake from the visitor's pier observed an orange luminous sphere appear on the water surface 50–100 meters from the island. The light moved gently for about two minutes, then faded. The priest stated: "This was not a floating lantern offering. No one could have been there; the ball shape was distinct."
Two more sightings were reported by the priest in September; five reports from tourist boat passengers followed in October. Boats connecting Chikubushima to various Biwa ports carry special evening and night-tour services in autumn. Passengers on these services reported seeing "balls of light floating near the island" in the dusk or post-sunset period.
A limnologist noted that autumn decomposition of aquatic vegetation in Lake Biwa produces increasing methane off-gassing, which occasionally ignites near the surface in a phenomenon called *koka* (lake fire). This is documented at other Japanese deep lakes. However, the stable sphere size of 50 cm–1 meter and simultaneous multiple appearance exceed typical lake fire descriptions; the researcher noted a supplementary explanation may be required.
Timeline
- Night of Sept 18, 2021Shrine priest observes an orange spherical light (50 cm–1 m) on the water surface near the island. Fades after ~2 min.
- September 2021Two more priest reports in the same month.
- October 2021Five tourist boat passenger reports of floating light spheres near the island in evening or after-dark conditions.
- November 2021Limnologist proposes lake fire (koka) hypothesis; notes scale exceeds typical lake fire.
- Autumn 2022Monitoring attempt at same season; one report only. Eight-in-one-month concentration does not recur.
- PresentCoordination with northern Lake Biwa lake-bottom gas survey under consideration.
Witness Testimony
Shrine priest (male, 50s)"From the pier I watched an orange sphere appear on the lake surface. Not a floating lantern — no one could have placed it there. I felt it was Benzaiten's light. Not frightening — sacred."
Tourist boat passenger (female, 40s)"When Chikubushima came into view, there were several points of light around the island. I thought it was surface reflection in the evening light, but the lights were rising from the surface. The person next to me saw them too."
Limnologist (male, 50s)"Combustible gas from lake bottom decomposition does occur in autumn and can ignite as small spherical flames near the surface — lake fire. But multiple simultaneous spheres at that scale is somewhat larger than the typical phenomenon."
Kyu's Analysis
At Benzaiten's sacred island, spherical lights float on the water. Multiple at once. They come in autumn and leave with autumn. Chikubushima runs its own lantern offerings.
