Tsugaru Strait (Tsugaru Kaikyo) is a channel between Honshu and Hokkaido in northern Japan connecting the Sea of Japan with the Pacific Ocean. It was named after the western part of Aomori Prefecture. The Seikan Tunnel passes under it at its narrowest point (19.5 km) between Tappi Misaki on the Tsugaru Peninsula in Aomori, Honshu and Shirakami Misaki on the Matsumae Peninsula in Hokkaido. The Tsugaru Strait is a one of 7 straits in the world.
Japan's territorial waters extend to three nautical miles (5.6 km) into the strait instead of the usual twelve, reportedly to allow nuclear-armed United States Navy warships and submarines to transit the strait without violating Japan's prohibition against nuclear weapons in its territory.
The Tsugaru Strait has eastern and western necks, both approximately 20 km across with maximum depths of 200 and 140 m respectively.
In the past, the most common way for passengers and freight to cross the strait was on ferries, approximately a four-hour journey. Now the Seikan Tunnel provides a convenient but more expensive alternative and approximately halves the travel time in comparison to ferrying. When Shinkansen trains can traverse the tunnel to Hakodate (scheduled for 2015), the journey time will be cut to 50 minutes.
On September 26, 1954 1,172 lives were lost when the ferry Toôya Maru sank in the strait.
Thomas Blakiston, an English explorer and naturalist, noticed that animals in Hokkaido were related to northern Asian species, whereas those on Honshu to the south were related to those from southern Asia. The Tsugaru Strait was therefore established as a major zoogeographical boundary, and became known as the "Blakiston Line