Cayuga is a Northern Iroquoian language of the Iroquois Proper (also known as "Five Nations Iroquois

Iroquois

The Iroquois , also known as the Haudenosaunee or the "People of the Longhouse", are an association of several tribes of indigenous people of North America...

") subfamily, and is spoken on Six Nations of the Grand River First Nation, Ontario, by around 100 Cayuga

Cayuga nation

The Cayuga people was one of the five original constituents of the Haudenosaunee , a confederacy of American Indians in New York. The Cayuga homeland lay in the Finger Lakes region along Cayuga Lake, between their league neighbors, the Onondaga to the east and the Seneca to the west...

 people.
There were at one time two distinct dialects of Cayuga. One is still spoken in Ontario, the other, called "Seneca-Cayuga," was spoken in Oklahoma until the 1980s.
There are two varieties of Cayuga.