Cai River
General data
- Name: Cai River
- Water system: Lagoa dos Patos
- Water type: River
- Progression: Guaiba River -> Lagoa dos Patos -> Rio Grande Channel -> Atlantic Ocean -> Planet Earth
- Climates: Tropical
- Continents: South America
- Countries: Brazil
The Caí River (Portuguese pronunciation: [kaˈi]) is a river of Rio Grande do Sul state in southern Brazil. It is a tributary of the Jacuí River, just above the junction with the Guaíba.