Outings and excursions · San Martín de los Andes
Arroyo Partido: the stream that flows into both the Atlantic and the Pacific
Photos: Gabriel Patiño (CC BY-SA 3.0, Wikimedia Commons)
On Route 40, about 20 km from San Martín de los Andes, a stream from the Chapelco range splits in two: one branch reaches the Atlantic and the other, through Chile, the Pacific.
About 20 kilometers from San Martín de los Andes, on Route 40 towards Villa La Angostura, there is a stream that cannot make up its mind about which ocean to reach. It comes down from the Chapelco range, runs under a road bridge and, just on the other side, a few rocks split it in two: one branch ends in the Atlantic Ocean and the other, after crossing the Andes into Chile, in the Pacific Ocean. That is why it is called Arroyo Partido, the "split stream".
A watershed in the middle of a streambed
A watershed, or drainage divide, is the line that separates two river basins: on one side the water flows to one sea, on the other side to another. It almost always runs along a ridge or a mountain range. At Arroyo Partido it runs right through the bed of the stream, something very rare in nature.
Where it comes from
It rises at about 2,000 meters above sea level in the Chapelco range, fed by springs and snowmelt from the summit. It flows west through the forest down to the Bajo de los Leones, crosses National Route 40 under a bridge and there, as it hits a few rocks, divides into two clearly separate branches.
The branch that goes to the Atlantic
The left branch becomes the Culebra stream ("snake"), which lives up to its name and winds its way to the Hermoso River, which carries it to Lake Meliquina. The water leaves the lake through the Meliquina River, which joins the Filo Hua Hum to form the Caleufú; the Caleufú flows into the Collón Curá, and the Collón Curá into the Limay. Where the Limay meets the Neuquén River, the Río Negro is born; it crosses the province of Río Negro from west to east and reaches the sea about 30 kilometers from Viedma, next to El Cóndor. All in all, more than 1,000 kilometers to the Atlantic.
The branch that goes to the Pacific
The right branch takes the name of Pil Pil stream and flows into Lake Lácar, the lake on whose shore San Martín de los Andes stands. Lake Lácar drains into Lake Nonthué, and from there the Hua Hum River crosses into Chile and reaches Lake Pirihueico. From there the water continues along the Fuy River and a chain of Chilean rivers and lakes (Panguipulli and Riñihue among them) to the San Pedro, Calle-Calle and Valdivia rivers, which flow into Corral Bay, on the Pacific Ocean. It is a basin shared by Argentina and Chile.
How to get there
From San Martín de los Andes, head south on National Route 40, the Seven Lakes Route. At kilometer 15 you pass the turnoff to Cerro Chapelco on your left; about 5 kilometers further on, on your right, there is a large wetland in the Pil Pil pass area. Next to the bridge, on the west side, is the Arroyo Partido viewpoint, with signs that explain the phenomenon. It is one of the classic stops along the route. In winter, a snow park run by the Mapuche Curruhuinca community operates next to the stream, inside Lanín National Park. See accommodation in San Martín de los Andes.
