Kase River Firefly Festival — June Bioluminescence

The Kase River and its tributaries in the southern Saga mountains host one of Kyushu's most concentrated firefly populations — the combination of clean water, low agricultural chemical use, and dense riparian vegetation has maintained conditions for Genji-botaru (the large Japanese firefly) that have disappeared from most of Japan. The firefly season runs June 1–20, and the peak nights (June 8–12 in an average year) see thousands of simultaneous light signals over the river.