| Açunguí River | |
| Pushpin Map: | Brazil |
| River System: | Ribeira de Iguape River |
| Source1 Location: | Paraná state |
| Source1 Coordinates: | -25.4671°N -49.7041°W |
| Mouth Coordinates: | -24.9063°N -49.4725°W |
| Subdivision Type1: | Country |
| Subdivision Name1: | Brazil |
The Açunguí River (Portuguese: Rio Açunguí) is a river of Paraná state in southern Brazil. It is a headwater of the Ribeira de Iguape River.
The Açungui river basin is the last natural reserve of unpolluted water to supply the metropolitan region of Curitiba.The basin includes the Açungui National Forest, created in 1944 under the government of Getúlio Vargas as the Romário Martins Park, with an area of .The national forest preserves araucarias.The river basin covers about .
The river rises in the foothills of the Serra de São Luiz do Purunã, Paraná.The river rises to the northwest of Curitiba and flows in a generally northeast direction to join the Ribeira River, which flows east into São Paulo.The Açungui valley is steep, with many small canyons and very close to the National Forest, so the environment has been well preserved.There are rapids along the river, particularly in the Canyon do Acalantilado, making it an excellent place for rafting.The Ribeira de Iguape River forms at the confluence of the Ribeirinha River and the Açungui River in the state of Paraná, less than from Curitiba.
The river's hydroelectric potential has been of interest since the 1950s, but the larger plants on the Iguaçu River gained priority.Large hydroelectric plants, with their large environmental impact, are now out of fashion, and the potential for a series of small hydroelectric plants along the Açungui was being considered in 2015.