The name of the river derives from the Ainutesh・o・pet meaning "river full of fishing weirs", perhaps because of rocks dotted across the river in such a shape. Alternatively, there is a locale in Bifuka that has been designated a municipal Historic Site as the "Place of Derivation of the Teshio River" on the basis that it was while staying here, during his exploration to the source of the river, on the seventh day of the sixth month of Ansei 4, there being a fishing weir at the spot, that Matsuura Takeshirō recorded the river's name. Due to works on the river in recent years the rocks in its middle course that perhaps inspired the name themselves largely no longer exist.
Geography
The river's source is at Mount Teshio, highest of the Kitami Mountains. Flowing down through the mountain valleys from its origins in Shibetsu, it is fed by tributaries including the Nayoro River, then crosses the mountain plains, passing next through the more constricted topography of Otoineppu, before entering the Teshio Plain, where it meanders, finally flowing into the Sea of Japan, in Teshio. The lower are, unusually, unbroken by dams and weirs and can be navigated uninterrupted. In the river basin, which has an area of, there are twelve municipalities:
As of the 2010 census, some 122,000 people lived in the basin.
History
It is believed the first humans arrived in the Teshio River system approximately fifteen thousand years ago. At the Kawaguchi Site in Teshio, where the river enters the Sea of Japan, remains of some two hundred and thirty pit dwellings have been discovered, with deposits of the Zoku-Jōmon period as well as of the Satsumon and Okhotsk cultures. Opening of the Teshio Trading Station, similarly at the mouth of the river, in Tenmei 6 marked the advent of the Wajin and their trade with the Ainu of the interior. The first survey of the river was conducted by three men under Takahashi Sōshirō, retainer of the Matsumae Domain, in Kansei 9, from its lower stretches as far as Otoineppu. In Ansei 4, Matsuura Takeshirō spent twenty-four days exploring the Teshio River, starting from its mouth; he subsequently wrote up his account of the river and those who lived along it in his Teshio Diaries. It was from the tales he heard from an Ainu elder living in the area of Otoineppu that Matsuura conceived of the name "Hokkaidō". Following the establishment of the Hokkaidō Development Commission in Meiji 2, settler-farmers began to arrive. After major floods in 1898, a need was identified for flood mitigation measures all over the island. After detailed surveying of the river between 1906 and 1908, and further flooding, a flood control plan for the Teshio River was first drafted in Taishō 8. There ensued a programme of bank reinforcement, embankment construction, and channel switching. After flooding continued to adversely affect the local farmers' potatoes, the Shōwa era saw further channel switching and the excavation of new waterways. A typhoon in 1981 and the heaviest rainfall since the war saw an area of inundated, with damage to 546 houses, while the typhoons of 2016 left 72 homes flooded. The river's history is documented at the Teshio River Historical Museum in Teshio.
Economy
In the upstream areas of Shibetsu and Shimokawa, the lumber industry exploits the abundant forests of the interior. The Nayoro basin between Nayoro and Bifuka marks the northern limit of rice cultivation. Downstream, on the Teshio Plain, there is dairy farming, while near the river mouth there is salmon and trout fishing and also the prefecture's most intensive harvesting of shijimi clams. Water sports include canoeing—there is an annual race "Daun za Tesshi o pet".
