Tseax River adopted in the 1930 BC Gazetteer, as labelled on Geological Survey map 69A, Route map of part of the Nass River, 1912, from the 1893 surveys of J.McEvoy, and as labelled on BC map 1H, 1917; confirmed 4 November 1948 on 103/ NE and 4 October 1951 on 103I. Form of name changed to Ksi Sii Aks per Nisga'a Treaty, Appendix F-3, effective 11 May 2000.

Source: BC place name cards, or correspondence to/from BC's Chief Geographer or BC Geographical Names Office

According to Nisga'a elders, "before the volcanic eruption, when our people lived here at Wii Lax K'ap, there was a stream close by where salmon spawned. The stream bed had white sand and they could easily spot the salmon going up stream. This stream was thus named Ksi Gimwits'ax. Years later [after the volcanic eruption] when this stream resurfaced, and though the Nisga'a knew it was the same tributary, it was renamed Ksi Sii Aks." [Ksi, in the context of geographical names, refers to "water flowing out from someplace"; Sii Aks means "new body of water".]

Source: Nisga'a Tribal Council / Ayuukhl Nisga'a Department, Aiyansh BC

It was also at this site where an historical event took place in the early 1900's, "the opening of a great smokehouse". This smokehouse belonged to the family of Ni'isyok, of Sii Aks. Today, the famous song composed for this event is one of the songs sung and performed by the Gitlaxt'aamiks Ceremonial Dancers. The song is called Git Sii Aks / People of the New Water.

Source: Nisga'a Tribal Council / Ayuukhl Nisga'a Department, Aiyansh BC