The Chuí, or Chuy, Stream (Portuguese: Arroio Chuí [ɐˈʁoju ʃuˈi], Rioplatense Spanish: Arroyo Chuy [aˈroʃo ˈtʃwi]), is a short stream on the Brazil–Uruguay border that is Brazil's southernmost point.

The Chui rises in a small swamp in the sandy coastal plains of the far southern Brazilian state of Rio Grande do Sul.

In Brazil, it lies mostly in the municipality of Santa Vitória do Palmar, with a short section in Chuí.

It would be unremarkable, were it not for the fact that it is known throughout Brazil and mentioned in all Brazilian geography schoolbooks as being the country's southernmost point.

It also marks the southern end of Cassino Beach, the world's longest uninterrupted stretch of sandy ocean shore, stretching over 240 km (150 mi) from the stone breakwaters of Rio Grande in its northern end.