The Ruvyironza (or Luvironza) River (French: rivière Ruvyironza) is a river in Burundi, the main tributary of the Ruvubu River. Its headwaters are the most remote source of the Nile when measured by river length from the Nile's mouth.

The Ruvyironza rises in the east of Bururi Province to the west of Mount Kikizi (2,145 metres (7,037 ft)). It forms near Kiryama and the RIG6 / RP83 junction, where its tributaries the Nyabuyugi and Kibazwa come together. It flows northwest to the border with Gitega Province. It follows part of the border between these two provinces, then flows through Gitega Province to the border with Mwaro Province, and follows the Mwaro-Gitega border north before turning east and again crossing Gitega Province to its mouth on the Ruvubu River. Most of the rivers in the Nile Basin portion of Burundi flow into the Ruvubu or its main tributary, the Ruvyironza.

The Luvironza River is the source of the Nile in the sense that it is in the Nile basin, and the distance by river from its headwater to the mouth of the Nile is 6,671 kilometres (4,145 mi), longer than the distance from any other headwater. It is a tributary of the Ruvubu River, a tributary of the Kagera River, which flows in Lake Victoria. From there, the river takes different names as it flows north: the Victoria Nile, Albert Nile, Bahr al Jabal, White Nile and north of Khartoum the Nile.

The surroundings of the upper Ruvyironza are mainly savannah. The area is quite densely populated, with 239 inhabitants per square kilometer as of 2016. The average annual temperature in the area is 20 °C (68 °F). The warmest month is September, when the average temperature is 23 °C (73 °F), and the coldest is April, with 18 °C (64 °F). Average annual rainfall is 1,137 millimetres (44.8 in). The wettest month is December, with an average of 199 millimetres (7.8 in) of precipitation, and the driest is July, with 1 millimetre (0.039 in) of precipitation.

At Nyabiraba in central Gitega Province the Ruvyironza has a 728 square kilometres (281 sq mi) drainage basin, with average flow of 10 cubic metres per second (350 cu ft/s). Annual preciptiation is 1,209 millimetres (47.6 in) and average temperature is 17.8 °C (64.0 °F). The laws regarding the public hydraulic zones are not respected in any of the Ruvubu watersheds, but particluarly along the Ruvyironza. This results in frequent landslides of the unprotected river banks.

The Ruvyironza basin contains 8,425 hectares (20,820 acres) of marshes, of which 7,310 hectares (18,100 acres), or 87%, were exploited for agriculture by 1998. The Ruvyironza flows along the eastern boundary of the Commune of Gishubi in Gitega, separting it from the Commune of Makebuko. The Kanyangwa River flows through Gishubi to join it from the west (left). The marshes of these two rivers are used for farming year round. The soil in this section of the river is not very fertile, and the farmers must use fertilizer.

In December 2015 torrential rains in the Commune of Mutaho, Gitega Province, devastated fields in the marshes of the Ruvubu and Ruvyironza rivers. Crops of beans, corn and sweet potatoes that had already been planted were lost. In April 2024 extensive flooding in the Ruvyironza River valley destroyed several hectares of crops in the Commune of Nyabihanga, Mwaro Province. The bridge linking the Commune of Nyabihanga to the Commune of Gitega was at risk of collapse.

The Ruvyironza power station is in Gitega Province, northeast of the city of Gitega, facing Karuzi Province over the Ruvubu River. It is fed by a canal running south from a dam on the Ruvyironza River near its mouth on the Ruvubu River. It discharges into the Ruvubu River. The Ruvyironza plant, owned by REGIDESO Burundi, was commissioned in 1980/1984. Power is supplied by three 425 KW turbines, delivering 1275 KW when all three are running, or 850 KW when just two are operational.

A 2012 report by the Ministry for Energy and Mines stated that potential developments on the Ruvyironza (Luvi 047, 039, 012) might be able to deliver 21.2MW.

• List of rivers of Burundi