The river that forms a natural border between Argentina and Paraguay is the Paraná River. This significant waterway stretches over 4,000 kilometers, making it one of the longest rivers in South America. Its basin supports diverse ecosystems and is essential for transportation and trade in the region. The Paraná River is also vital for regional agriculture, providing irrigation to fertile lands. The river fosters rich biodiversity, including various fish species and wildlife, while also serving as a crucial resource for the communities living along its banks.