Nagara River

The Nagara River runs 166 kilometers through Gifu Prefecture and is considered one of Japan's cleanest rivers despite flowing through a city of 400,000 people. Each spring, small ayu sweetfish gather at the river's mouth after wintering at sea and swim upstream to stake out individual feeding territories on the gravelly riverbed. They spend summer alone, grazing on algae and leaving distinctive scrape marks on river stones. In autumn, rising floodwaters prompt them to school again and spawn near Gifu City. The river also supports the Japanese giant salamander and rare migratory species helped by fish runs installed in the downstream dam.