The Iriri River (Portuguese: Rio Iriri) is a large tributary of the Xingu River in Brazil, in the state of Pará. It is 1,300 km (810 mi) long making it the 116th longest river in the world (with Krishna River, India) and the 15th longest in the Amazon basin. The headwaters are the traditional home of the Panará people.
The river rises in the 342,192 hectares (845,570 acres) Nascentes da Serra do Cachimbo Biological Reserve, a strictly protected conservation unit established in 2005 in the Serra do Cachimbo. It is one of the headwaters of the Xingu River. It flows for 900 kilometres (560 mi) before joining the Xingu, running through the 3,373,133.89 hectares (8,335,195.4 acres) Terra do Meio Ecological Station. The river varies greatly in volume depending on the season, and in the dry season include waterfalls, rocks and rapids.
The Iriri River is rich in fish, including many species found only here and in the Xingu. Large sections remain unexplored due to its remoteness in a region surrounded by Amazon rainforest, and sections with strong current and cataracts.