| Alegre | |
| Pushpin Map: | Brazil |
| River System: | Guaporé River |
| Source1 Location: | Serra de Santa Bárbara State Park |
| Mouth Coordinates: | -15.0291°N -59.9683°W |
| Subdivision Type1: | Country |
| Subdivision Name1: | Brazil |
The Alegre River (Portuguese: Rio Alegre) is a river in the state of Mato Grosso, Brazil.
The Alegre River rises in the Serra de Santa Bárbara State Park, created in 1997.It flows in a generally northwest direction, receiving the Barbado River on its left, then flows north until it joins the Guaporé River from the left.