Swimmers in the Travesía Internacional de Natación Río Guadiana cross 2 kilometers of border water between Spain and Portugal. The race links Ayamonte in Andalusia with Vila Real de Santo António in the Algarve, and it runs each year as an open-water swim rather than a pool event. The start and finish swap sides annually, so one edition begins in Spain and the next begins in Portugal.
Around 250 swimmers are expected, which makes it large enough to feel like a proper mass swim but still tied closely to the two river towns. The Ayamonte City Council and the Naval Association of the Guadiana in Vila Real de Santo António organize it together. It also counts toward the Huelva Open Water Circuit, drawing circuit swimmers as well as people attracted by the unusual chance to race across international waters.