Maratón Internacional Hernandarias – Paraná (or the Maraton Nautica Internacional Hernandarias – Parana or Maraton Internacional de Rio Abierto) is held from the city Hernandarias to Paraná, Argentina in the Paraná River. At 88 km (54.6 mi), it is the longest open water swimming competition and longest professional marathon race in the world. Started in 1965, it is held annually in February under extremely competitive conditions, attracting the fastest marathon swimmers in the world, down a river with varying currents and flotsam. Tens of thousands of spectators line the course in an extremely festive atmosphere. Offers US$25,000 in prize money when it is part of the global FINA Open Water Swimming Grand Prix circuit.