The Ksi Sii Aks (formerly Tseax River) is a tributary of the

Nass River The Nass River is a river in northern British Columbia, Canada. It flows from the Coast Mountains southwest to Nass Bay, a sidewater of Portland Inlet, which connects to the North Pacific Ocean via the Dixon Entrance. Nass Bay joins Portland Inl ...

in northwestern

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

, Canada. It is most notable as the namesake of

Tseax Cone The Tseax Cone ( ), also called the Tseax River Cone or the Aiyansh Volcano, is a young and active cinder cone and adjacent lava flows associated with the Nass Ranges and the Northern Cordilleran Volcanic Province. It is located east of Crater C ...

, a

volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates are ...

within its basin that was responsible for an eruption in the 17th century that killed 2,000 Nisga'a people. Prior to the eruption, the

Nisga'a The Nisga’a , often formerly spelled Nishga and spelled in the Nisga'a language as (pronounced ), are an Indigenous people of Canada in British Columbia. They reside in the Nass River valley of northwestern British Columbia. The name is a r ...

name for this river was Ksi Gimwits'ax. Buried by the eruption, it eventually resurfaced. The Nisga'a recognized it as the same stream but renamed it Ksi Sii Aks: means "new body of water". As prescribed by terms of the

Nisga'a Treaty The Nisga'a Final Agreement, also known as the Nisga'a Treaty, is a treaty that was settled between the Nisg̱a'a, the government of British Columbia, and the Government of Canada that was signed on 27 May 1998 and came into effect on May 11, 2000 ...

, the Tseax River is now officially named the Ksi Sii Aks. Ksi Sii Aks flows about north to the Nass River.Length measured using Google Maps path tool, BCGNIS coordinates, topographic maps, an
TopoQuest
From its source near Sand Lake the river flows through Sand Lake, Gainor Lake, and Lava Lake. It collects many tributary streams, the largest of which are Poupard Creek, May Creek, Alder Creek, Crater Creek, Auk Creek, and Gitzyon Creek.

References

Nass Country Rivers of British Columbia Cassiar Land District {{BritishColumbiaInterior-river-stub