Misiones Aguas Abiertas

Misiones Aguas Abiertas is an individual open water swimming marathon contested along the city shoreline of Posadas, in the province of Misiones, Argentina. The competition takes place entirely in the freshwater currents of the Paraná River, challenging body and mind across a demanding course. Organized by Club Náutico León Seró alongside the Asociación Tri Misiones, the race was relaunched in 2025 to revive the legacy of the historic Cruce del Paraná, an open water event that had remained suspended since 2010. The marathon covers an exact distance of 10,000 meters along a course charted parallel to the Posadas city coastline. Swimmers launch into the river current from Balneario Costa Sur and navigate the coastal line until reaching the arrival arch at Balneario El Brete.

To ensure safety over this sustained distance, the route through the Paraná River is carefully designed to avoid dangerous areas such as the immediate shoreline, submerged logs, and rocks. The arrival became a moving homecoming when family members were invited onto the beach to present the commemorative Desafío Superado medals directly to the athletes. Reaching the final cove after hours of continuous effort brings a profound sense of accomplishment as the river journey comes to an end.

On the Paraná: guides, boats and the 2025 relaunch

The 2025 edition of Misiones Aguas Abiertas drew 24 competitors from various points of the tierra colorada and from neighbouring provinces. Each swimmer in the 2025 Misiones Aguas Abiertas had a guide in a canoe, boat, stand-up paddleboard or sit-on-top kayak for the whole course. Tri Misiones reported that six motorised boats were used during the 2025 Misiones Aguas Abiertas. Jorge Noguera and Constanza Guimarez won the 2025 Misiones Aguas Abiertas, a 10 km swim between the Costa Sur and El Brete beaches in Posadas. Swimmers at Misiones Aguas Abiertas receive a personalised safety buoy bearing the event's crest.

The Paraná River: ancient paleochannels and the reservoir waters

Ancient drainage networks show that the Paraná once flowed toward the Uruguay River through the channels of what are today the Garupá, Pindapoy, and Aguapey streams. In fact, part of the modern Pindapoy Grande stream represents a surviving paleochannel of that original Paraná course. The Pindapoy Grande stream originates in the San José mountain range and flows until it feeds into the Garupá stream. Along its route, the Pindapoy Grande receives the Tororó and Pindapoy Chico streams on its left bank, while the Guasupí stream joins from its right bank. The receiving Garupá stream, situated about ten kilometres from the race area, acts as a direct tributary of the Paraná River.

It extends for a total length of 32.06 kilometers across a basin covering 1,416 square kilometers, and its course was historically recorded in Jesuit cartography during the expansion of the regional missions. Local residents report that the Garupá stream frequently overflows during periods of heavy rainfall, reflecting the powerful water dynamics of the regional basin. Hydroelectric works carried out under the Yacyretá project raised the river's water level from 76 meters to 83 meters above sea level. This rise in water level reached far into regional tributaries, including the Zaimán stream, which originates at Estancia San Francisco and flows into the Paraná River. The Zaimán forms a natural boundary between the municipalities of Posadas and Garupá from its source to its confluence with the Lapacho stream.

Following the construction of the dam, the water level of the Zaimán also rose to 83 meters above sea level, producing a broad 200-hectare lake at its mouth. Managing these expanded waters required extensive coastal protection works and a small coastal avenue, which involved the relocation of over 300 properties.

San Roque González de Santa Cruz Bridge: swimming under the international span

About five kilometres from the race area, the Paraná River is crossed by the San Roque González de Santa Cruz Bridge. This major structure spans the river across the international boundary, connecting the city of Posadas in Argentina with the city of Encarnación in Paraguay. The crossing was proposed in 1977 as formal compensation to Paraguay for the territorial flooding caused by the Yacyretá Dam reservoir. The bridge structure measures 2,550 meters in total length, anchored by a 570-meter main span and a 1,595-meter approach viaduct. Across the international border in Encarnación, the river is lined by the Avenida Costanera, which stretches for 27 kilometers along the banks of the Paraná and its surrounding streams.

This Paraguayan riverfront was developed under the Yacyretá Termination Plan to accompany the rise of the river to 83 meters, recovering 140 hectares of land that would have otherwise been submerged by the reservoir. The coastal avenue in Encarnación opened in stages, starting with the Padre Bolik sector, which measures 800 meters in length and 100 meters in width. Farther along the Paraguayan shoreline, the Naval Detachment of Encarnación sits in the Mbói Ka'e neighborhood, located just meters from the beach.

Reserva Natural Urbana Arroyo Itá: river biodiversity at Bahía El Brete

About six kilometres from the race area, at the mouth of the Itá stream where it empties into the Paraná River at El Brete bay, lies the Reserva Natural Urbana Arroyo Itá. The protected area encompasses 2.8 hectares and was established in 2013 following the 2011 rise in water levels generated by the Yacyretá Reservoir. The reserve preserves the wetland ecosystem that formed where the stream meets the wide river basin. The floating aquatic vegetation within this river mouth includes dense patches of water hyacinths, water lentils, and water ferns. A total of 40 species of fish enter the stream from the Paraná River, including river corvinas. The marathon swim is charted out in the open river channel.

Costanera Monseñor Kemerer: the riverfront avenue framing the course

Flanking the swim course along the Argentine shore is the Costanera Monseñor Kemerer, an avenue that borders the Paraná River throughout the city of Posadas. The avenue was built as part of the complementary infrastructure works carried out for the Yacyretá Dam project. Constructing this extensive urban riverfront required significant changes along the waterfront, including the relocation of residents who previously lived directly on the riverbanks. Under one kilometre from the race area sits the Alberto Roth botanical garden. This green space is situated directly at the mouth of the Zaimán stream where it flows into the Paraná River. The swim concludes at the La Bahía El Brete sector, which was inaugurated in 2011 with a wide beach area.

Under normal regulations, casual swimming in the Paraná River is prohibited at this beach. For the Misiones Aguas Abiertas competition, however, the bay becomes an organized finish arena, welcoming swimmers out of the ten-kilometer river test to celebrate with their families right on the sand.