San Antonio Oeste tide times

San Antonio Oeste is a small port town at the inner end of the San Matías Gulf, 14 km northeast of Las Grutas. It is the reference tide gauge station for the northern Patagonian coast and the site of one of the largest tidal ranges in South America: spring range at San Antonio Oeste is 6.0–7.0 m above Chart Datum, driven by the funnel geometry of the San Matías Gulf concentrating the Patagonian shelf tidal prism into an increasingly narrow basin.

The tidal flat at San Antonio Oeste is extraordinary. At spring low water, the sea retreats roughly 3–5 km from the town shore; the exposed flat is a broad expanse of compacted sand and mud that remains wet and soft in the channels but is firm enough to walk on the higher sand areas. During February and March, this tidal flat is one of the most important shorebird staging areas in the Western Hemisphere. Red knot (Calidris canutus rufa) — a small wader that breeds in the Canadian high Arctic and overwinters in Tierra del Fuego — staggers its northward migration through San Antonio Oeste, fuelling on the extraordinary density of bivalves (Darina solenoides, a small clam) in the flat's upper intertidal zone. Counts of 40,000–60,000 red knot on the San Antonio flats in February–March have been recorded; along with similar numbers of sanderlings, dunlin, and other sandpipers.

The port at San Antonio Oeste handles fish processing, supply to the oil and gas operations in the Neuquén basin (via road connections inland), and some general cargo. The port access and the commercial dock are tidal-dependent: vessels enter and depart within a tide window around the high. The town itself sits above the high-water line; the land drops steeply to the tidal flat at the shoreline.

For visitors interested in the shorebird migration, the most productive viewing is from the high-water line at rising tide, when the flood pushes the birds off the flat and concentrates them on the upper beach in tight flocks. At low water the birds spread across the vast flat and individual species are harder to pick out. Binoculars are essential; telescope desirable. SHN Argentina has a permanent tide gauge at San Antonio Oeste — the official reference station for the San Matías Gulf. Tide predictions here come from Open-Meteo Marine: accuracy ±45 min / ±0.2–0.3 m.

The Área Natural Protegida Bahía San Antonio was created in 2001 specifically to protect the shorebird staging habitat; the designation covers the tidal flat, the surrounding salt marsh, and the coastal dune system. BirdLife International has designated the San Antonio Bay as an Important Bird and Biodiversity Area (IBA). The WHSRN (Western Hemisphere Shorebird Reserve Network) has listed San Antonio Bay as a site of hemispheric importance, recognising that the loss of this habitat would affect migratory shorebird populations across two continents. Visiting in February–March specifically to observe the red knot migration requires binoculars and ideally a telescope; the flock densities are high enough that even without optical aid the cloud of birds at high-water roosting is visible from the beach access road.

The shorebird migration at San Antonio has attracted international ornithological attention since the 1980s; the site appears on the migration route maps of every major shorebird conservation organisation. The journey of the red knot subspecies rufa — breeding in the Canadian Arctic, wintering in Tierra del Fuego, staging at San Antonio and other South American sites — has been described as one of the longest migrations relative to body size in the animal kingdom. Satellite transmitter tracking studies have shown individual red knots making 8,000 km non-stop flights over the Atlantic between the Tierra del Fuego wintering grounds and the North American staging areas.