Which river system is listed eighth by length and includes the Paraná River?

The river system listed eighth by length and including the Paraná River is the Río de la Plata system.

This system is commonly measured from the headwaters of the Rio Grande in Brazil through the Paraná River and onward to the Río de la Plata estuary. The Paraná joins the Uruguay River near the coast, and their combined waters form the broad Río de la Plata before reaching the Atlantic Ocean. Length rankings treat this as a connected river system rather than measuring only the named estuary.

The system extends across Brazil, Argentina, Paraguay, Bolivia, and Uruguay, with a drainage basin covering about 3.18 million square kilometres. A common mix-up is confusing the Río de la Plata system with the Paraná alone: the Paraná is its principal river, but the ranking refers to the complete connected system. The Río de la Plata is also sometimes called a river and sometimes an estuary, depending on the classification used.