The Matanza River is known by several names, including, in Spanish, Río de la Matanza ("the slaughter river" in English), Río Matanza ("slaughter river"), Río Mataderos ("slaughterhouses river"), Río de la Manzana ("the apple river") or simply Riachuelo ("little river" or "brook"). It is a 64-kilometre (40 mi) stream in Argentina that originates in the Buenos Aires Province and defines the southern boundary of the Buenos Aires federal district. It empties into the Río de la Plata between Tandanor and Dock Sud. The La Boca neighbourhood and the Boca Juniors football club are located near the Riachuelo's mouth. The Spanish word boca means "mouth".
From its source down to La Noria Bridge on Avenida General Paz, the river is usually referred to as Río La Matanza, and from that point onwards as Riachuelo. Approximately 3.5 million people live in its drainage basin of 2,240 km2 (865 sq mi).
The south-easterly storm wind, known as Sudestada, hinders the waters of the Riachuelo from reaching the Río de la Plata, producing frequent flooding in low-lying areas like La Boca and Barracas. Since 1995 a number of flood control projects have been carried out to prevent such occurrences.
The Matanza's main tributaries are the Cañuelas, Chacón, and Morales streams in the Province of Buenos Aires, and the Cildáñez stream (currently piped) in the Greater Buenos Aires urban area. The Matanza receives large amounts of industrial waste from the numerous factories along the river, especially tanneries, which makes the Matanza/Riachuelo a polluted river. Among the most dangerous contaminants are heavy metals and waste water from the basin's saturated layers. A contentious political subject since at least the 1862-68 administration of President Bartolomé Mitre, the Riachuelo's plight has attracted the attention of other public figures, notably artist and Greenpeace activist Nicolás García Uriburu, who dyed the waterway green in 1970, and on World Water Day (March 22) in 2010, to draw attention to the problem.
In 1993 President Carlos Menem's Secretary of Environment María Julia Alsogaray presented a 3-year project to clean up the Riachuelo that was approved, but never started, let alone concluded. The former civil servant, daughter of conservative policy maker Álvaro Alsogaray, was prosecuted for misappropriation of those public funds.
According to Argentine newspaper Página/12, of the 250-million-dollar budget, only $90 million remain; $6 million were lost in punitive interests, $150 million were destined to unrelated social projects, and only $1 million was used for the actual cleanup. Critics have also noted that this cleanup was in vain, as all that was done was to remove sunken ship hulls, but nothing was done to prevent newly abandoned ships from sinking. A period of optimism regarding the waterway's condition followed announcements in 2006 by President Néstor Kirchner that the Riachuelo's improvement would be prioritized; but, though some efforts were undertaken, the river remains a source of health problems and urban blight for its adjoining neighborhoods. Environmental cleanup efforts have been supplemented by urban renewal proposals for the area.
See also 
- Río de la Matanza at GEOnet Names Server
- Río Matanza at GEOnet Names Server
- Río Mataderos at GEOnet Names Server
- Río de la Manzana at GEOnet Names Server
- Riachuelo at GEOnet Names Server
- Autoridad de Cuenca Matanza Riachuelo (Spanish)
- Arte al Día: Nicolás García Uriburu (Spanish)
- Clarín: Del esplendor de los noventa a la acumulación de causas penales (Spanish)
- (Spanish) Página/12 (Spanish)
- IPS News: Riachuelo Clean-Up Plan Sparks Hope
- Clarín: Los planes para el Riachuelo (Spanish)
- GNS coordinates adjusted using Google Maps and GeoLocator