[1][6] It is most notable as the namesake of Tseax Cone, a volcano within its basin that was responsible for an eruption in the 17th century that killed 2,000 Nisgaʼa people.

Prior to the eruption, the Nisgaʼa name for this river was Ksi Gimwitsʼax.

[1] As prescribed by terms of the Nisgaʼa Treaty, the Tseax River was officially renamed the Ksi Sii Aks on 11 May 2000.

[6] Ksi Sii Aks flows about 45 km (28 mi) north to the Nass River.

This article related to a river in the Interior of British Columbia, Canada is a stub.