The Guaíba Lake is a waterway in Rio Grande do Sul, a state in southern Brazil. It is famous for its beautiful reflection at sunset. The Guaíba is an extension of the Lagoa dos Patos, a huge coastal lagoon to the south, and although commonly referred to as a "river", the Guaíba is an estuary, and is also referred to as a bay, lake, or lagoon. The Jacuí River empties into the Guaíba from the north.