Rio do Peixe is a river in the state of Santa Catarina, in southern Brazil, flowing approximately 249 to 299 kilometers from its headwaters at Serra da Taquara Verde, at an elevation of around 1,250 meters, down to its confluence with the rio Uruguai at roughly 387 meters elevation, near the town of Marcelino Ramos in Rio Grande do Sul. The river drains a basin of approximately 5,238 to 5,277 square kilometers and is part of the broader Plata basin system.

The river passes through a number of municipalities in the interior of Santa Catarina, including Calmon, Caçador, Videira, Joaçaba, Herval d'Oeste, and Capinzal, among others. A railway line connecting São Paulo and Porto Alegre runs along the left bank of the river. The main tributaries are the rio Limeira and the rio Estreito.

The river's name historically referred to the abundance of fish once found in its waters. However, the river is currently significantly polluted and ecologically degraded. This is a critical consideration for anyone planning to paddle here, as water contact carries potential health risks. Remediation programs are underway, but the overall water quality remains a serious concern. Paddlers should research current conditions carefully before any trip and take appropriate precautions regarding water contact.

The river's considerable elevation drop over its length — from 1,250 meters at the source to 387 meters at the mouth — suggests varied gradient and potentially moving water in its upper reaches, though the specific nature of rapids, portages, or technical difficulty remains unclear without direct reconnaissance.