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Setonaikai NP, Hyogo / Tokushima
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Naruto’s eddies can appear in a vanishing chain: as many as 7 may line up, each lasting just 20–30 seconds. Its “uzutsui” are paired whirlpools spinning in opposite directions beside the central current.
A 1.5m water-level step can form across the strait: one tide arrives directly, while another loops around Awaji via Akashi and takes about 6 hours to catch up, driving currents up to 20km/h.
Fishing trawls have hauled Naumann’s elephant teeth and deer antlers from the Naruto seabed. Tokushima Prefectural Museum says they point to a time when the Seto Inland Sea was dry land.
A hard Cretaceous sandstone ridge crosses about 1.4km of seabed between the headlands. Currents have also carved two bowl-shaped hollows nearby, deeper than 160m and 210m.
A Nara-period wooden tag from Heijō Palace records a basket of wakame sent as tribute from Mūya Sea, in today’s Naruto area. Local seaweed was reaching Japan’s capital more than 1,000 years ago.
Local history credits Naruto trader Maekawa Buntarō with developing ash-dried wakame in 1845. The seaweed was coated with plant ash, dried, then washed and dried again—a method valued for preserving its color.
A knobby vertebral bone sometimes found in Naruto sea bream is nicknamed “Naruto bone.” A 1697 account blamed the rapids; a Tokushima Museum study identifies it as thickened bone and notes it also occurs elsewhere.
A high-resolution 2020 ocean model found that the whirlpool zone also drives plunging vertical circulation beneath the surface, mixing water efficiently and helping move it from Harima-nada toward Kii Channel.
Naruto’s long, slim kanko boats had sharply upswept prows, shaped to reduce drag and ease steering in the strong current. They served local fishers until engine-powered fiberglass boats spread in the 1970s.
Before wakame farming, wild harvest began on a designated opening day. Fishers rowed kanko boats to reefs and peered through a hakomegane—an underwater viewing box—before cutting the seaweed.
In 935, the Tosa Diary records travelers leaving Tosa-domari after dark to cross “Awa no Mito,” the old name for Naruto Strait. They had heard pirates did not travel at night and prayed as they crossed.
A local book from 1734 and other Edo-period records reported mermaids visiting Naruto Strait. One modern interpretation suggests distant dugongs or finless porpoises may have inspired the sightings; it is not a settled identification.
Utagawa Hiroshige depicted Naruto’s whirlpools in a woodblock print around 1853. Japan’s tourism agency notes that ukiyo-e and 19th-century traveler Philipp Franz von Siebold helped introduce the spectacle to Europeans.
The Hachisuka lords sailed from Tokushima Castle to watch Naruto’s whirlpools. They built a temporary teahouse at the viewpoint now called Ochaen—literally, the “tea garden.”
Ōnaruto Bridge was designed with a lower level that could carry a railway beneath its road deck. Today, that space holds the 450m Uzu-no-Michi walkway, suspended above the strait.
Although the strait is about 1.3km across, its navigable passage is only about 400m wide. In 2012, the Coast Guard began sending current information to crossing ships via AIS, as currents can reach 11 knots.
One official interpretation reads “Naruto” as a “roaring gate”: “naru” evokes the thunder of rushing water, while “to” refers to the narrow sea entrance between the capes.
