The Paraná flows north–south and becomes an alluvial basin (a flood plain) between the Argentine provinces of Entre Ríos, Santa Fe and Buenos Aires then emptying into the Río de la Plata.

It covers about 14,000 square kilometres (5,400 sq mi) and starts to form between the cities of Santa Fe and Rosario, where the river splits into several arms, creating a network of islands and wetlands.

The Lower Delta was the site of the first modern settlements in the Paraná-Plata basin and is today densely populated, being the agricultural and industrial core of Argentina and host to several major ports.

The main course of the Paraná lies on the west of the delta, and is navigable downstream from Puerto General San Martín by ships up to Panamax kind.

As in the entire Pampas region, summers are "cut" by short, cool periods when southerly Pampero winds blow.

As in the entire Pampas region, there are often brief, mild spells in the winter when the temperatures might reach 25 °C (77F), followed by much colder weather and frosty nights.

The original ecosystem, especially in the Lower Delta, has been heavily modified by deforestation, hunting, fishing and the introduction of foreign species of flora, as well as damaged by domestic and industrial pollution.

It hosts species such as the marsh deer, the capybara, the neotropical river otter, the Pampas cat, the jaguar, the coypu and the red-faced guan, some of them endangered.

The establishment of the Biosphere Reserve aims at revitalizing the economy of the region at the same time as conserving the natural and cultural values of the area and support the investigation and study of the ecosystem with the possibilities of national and international investment in projects of sustainable growth and the grouping of the region in reference of organic cultivation and varied ways of land-forest production with certification of ecological quality.