The Pat River (Rivière à Pat) is a tributary on the east bank of the Nicolet Southwest River.

It crosses the municipalities of Sainte-Élizabeth-de-Warwick, Sainte-Séraphine and Sainte-Clotilde-de-Horton in the Arthabaska Regional County Municipality (MRC), in the administrative region of Estrie, in Quebec, in Canada.

The main neighboring hydrographic slopes of the Pat river are: The Rivière à Pat originates from various streams in the municipality of Sainte-Élizabeth-de-Warwick, very close to the limit of the municipality of Kingsey Falls.

From its source, Pat's River flows on 18.4 kilometres (11.4 mi) in the following segments: The Rivière à Pat drains on the east bank of the Nicolet Southwest River.

The toponym "Rivière à Pat" was formalized on September 5, 1985, at the Commission de toponymie du Québec.